failed tests
I'm running on Windows 7 32-bit, with Python 2.7.2. Dependencies installed, pandas cloned and built. 

Here is the output when I run "nosetests pandas" :

................SS.........S...............S.................C:\Python27\lib\site-packages\scikits\statsmodels\tools\tools.py:256: FutureWarning: The default of `prepend` will be changed to True in the next release, use explicit prepend
  "next release, use explicit prepend", FutureWarning)
...........S...................EEEEEE...............SS.....................C:\Users\candre4\pandas\pandas\core\index.py:441: RuntimeWarning: tp_compare didn't return -1 or -2 for exception
  return self.view(np.ndarray).argsort(_args, *_kwargs)
# .........S.................................S.......................S......
## ERROR: test_line_plot_datetime_frame (pandas.tseries.tests.test_plotting.TestTSPlot)

Traceback (most recent call last):
  File "C:\Users\candre4\pandas\pandas\tseries\tests\test_plotting.py", line 82, in test_line_plot_datetime_frame
    _check_plot_works(df.plot, freq)
  File "C:\Users\candre4\pandas\pandas\tseries\tests\test_plotting.py", line 118, in _check_plot_works
    plt.savefig(PNG_PATH)
  File "C:\Python27\lib\site-packages\matplotlib\pyplot.py", line 363, in savefig
    return fig.savefig(_args, *_kwargs)
  File "C:\Python27\lib\site-packages\matplotlib\figure.py", line 1084, in savefig
    self.canvas.print_figure(_args, *_kwargs)
  File "C:\Python27\lib\site-packages\matplotlib\backend_bases.py", line 1923, in print_figure
    *_kwargs)
  File "C:\Python27\lib\site-packages\matplotlib\backends\backend_agg.py", line 438, in print_png
    FigureCanvasAgg.draw(self)
  File "C:\Python27\lib\site-packages\matplotlib\backends\backend_agg.py", line 394, in draw
    self.figure.draw(self.renderer)
  File "C:\Python27\lib\site-packages\matplotlib\artist.py", line 55, in draw_wrapper
    draw(artist, renderer, *args, *_kwargs)
  File "C:\Python27\lib\site-packages\matplotlib\figure.py", line 798, in draw
    func(_args)
  File "C:\Python27\lib\site-packages\matplotlib\artist.py", line 55, in draw_wrapper
    draw(artist, renderer, *args, *_kwargs)
  File "C:\Python27\lib\site-packages\matplotlib\axes.py", line 1946, in draw
    a.draw(renderer)
  File "C:\Python27\lib\site-packages\matplotlib\artist.py", line 55, in draw_wrapper
    draw(artist, renderer, _args, *_kwargs)
  File "C:\Python27\lib\site-packages\matplotlib\axis.py", line 971, in draw
    tick_tups = [ t for t in self.iter_ticks()]
  File "C:\Python27\lib\site-packages\matplotlib\axis.py", line 907, in iter_ticks
    majorLabels = [self.major.formatter(val, i) for i, val in enumerate(majorLocs)]
  File "C:\Users\candre4\pandas\pandas\tseries\plotting.py", line 812, in __call__
    return Period(ordinal=int(x), freq=self.freq).strftime(fmt)
  File "C:\Users\candre4\pandas\pandas\tseries\period.py", line 101, in **init**
    raise ValueError("Ordinal must be positive")
ValueError: Ordinal must be positive
# 
## ERROR: test_line_plot_datetime_series (pandas.tseries.tests.test_plotting.TestTSPlot)

Traceback (most recent call last):
  File "C:\Users\candre4\pandas\pandas\tseries\tests\test_plotting.py", line 71, in test_line_plot_datetime_series
    _check_plot_works(s.plot, s.index.freq.rule_code)
  File "C:\Users\candre4\pandas\pandas\tseries\tests\test_plotting.py", line 118, in _check_plot_works
    plt.savefig(PNG_PATH)
  File "C:\Python27\lib\site-packages\matplotlib\pyplot.py", line 363, in savefig
    return fig.savefig(_args, *_kwargs)
  File "C:\Python27\lib\site-packages\matplotlib\figure.py", line 1084, in savefig
    self.canvas.print_figure(_args, *_kwargs)
  File "C:\Python27\lib\site-packages\matplotlib\backend_bases.py", line 1923, in print_figure
    *_kwargs)
  File "C:\Python27\lib\site-packages\matplotlib\backends\backend_agg.py", line 438, in print_png
    FigureCanvasAgg.draw(self)
  File "C:\Python27\lib\site-packages\matplotlib\backends\backend_agg.py", line 394, in draw
    self.figure.draw(self.renderer)
  File "C:\Python27\lib\site-packages\matplotlib\artist.py", line 55, in draw_wrapper
    draw(artist, renderer, *args, *_kwargs)
  File "C:\Python27\lib\site-packages\matplotlib\figure.py", line 798, in draw
    func(_args)
  File "C:\Python27\lib\site-packages\matplotlib\artist.py", line 55, in draw_wrapper
    draw(artist, renderer, *args, *_kwargs)
  File "C:\Python27\lib\site-packages\matplotlib\axes.py", line 1946, in draw
    a.draw(renderer)
  File "C:\Python27\lib\site-packages\matplotlib\artist.py", line 55, in draw_wrapper
    draw(artist, renderer, _args, *_kwargs)
  File "C:\Python27\lib\site-packages\matplotlib\axis.py", line 971, in draw
    tick_tups = [ t for t in self.iter_ticks()]
  File "C:\Python27\lib\site-packages\matplotlib\axis.py", line 907, in iter_ticks
    majorLabels = [self.major.formatter(val, i) for i, val in enumerate(majorLocs)]
  File "C:\Users\candre4\pandas\pandas\tseries\plotting.py", line 812, in __call__
    return Period(ordinal=int(x), freq=self.freq).strftime(fmt)
  File "C:\Users\candre4\pandas\pandas\tseries\period.py", line 101, in **init**
    raise ValueError("Ordinal must be positive")
ValueError: Ordinal must be positive
# 
## ERROR: test_line_plot_inferred_freq (pandas.tseries.tests.test_plotting.TestTSPlot)

Traceback (most recent call last):
  File "C:\Users\candre4\pandas\pandas\tseries\tests\test_plotting.py", line 88, in test_line_plot_inferred_freq
    _check_plot_works(ser.plot, ser.index.inferred_freq)
  File "C:\Users\candre4\pandas\pandas\tseries\tests\test_plotting.py", line 118, in _check_plot_works
    plt.savefig(PNG_PATH)
  File "C:\Python27\lib\site-packages\matplotlib\pyplot.py", line 363, in savefig
    return fig.savefig(_args, *_kwargs)
  File "C:\Python27\lib\site-packages\matplotlib\figure.py", line 1084, in savefig
    self.canvas.print_figure(_args, *_kwargs)
  File "C:\Python27\lib\site-packages\matplotlib\backend_bases.py", line 1923, in print_figure
    *_kwargs)
  File "C:\Python27\lib\site-packages\matplotlib\backends\backend_agg.py", line 438, in print_png
    FigureCanvasAgg.draw(self)
  File "C:\Python27\lib\site-packages\matplotlib\backends\backend_agg.py", line 394, in draw
    self.figure.draw(self.renderer)
  File "C:\Python27\lib\site-packages\matplotlib\artist.py", line 55, in draw_wrapper
    draw(artist, renderer, *args, *_kwargs)
  File "C:\Python27\lib\site-packages\matplotlib\figure.py", line 798, in draw
    func(_args)
  File "C:\Python27\lib\site-packages\matplotlib\artist.py", line 55, in draw_wrapper
    draw(artist, renderer, *args, *_kwargs)
  File "C:\Python27\lib\site-packages\matplotlib\axes.py", line 1946, in draw
    a.draw(renderer)
  File "C:\Python27\lib\site-packages\matplotlib\artist.py", line 55, in draw_wrapper
    draw(artist, renderer, _args, *_kwargs)
  File "C:\Python27\lib\site-packages\matplotlib\axis.py", line 971, in draw
    tick_tups = [ t for t in self.iter_ticks()]
  File "C:\Python27\lib\site-packages\matplotlib\axis.py", line 907, in iter_ticks
    majorLabels = [self.major.formatter(val, i) for i, val in enumerate(majorLocs)]
  File "C:\Users\candre4\pandas\pandas\tseries\plotting.py", line 812, in __call__
    return Period(ordinal=int(x), freq=self.freq).strftime(fmt)
  File "C:\Users\candre4\pandas\pandas\tseries\period.py", line 101, in **init**
    raise ValueError("Ordinal must be positive")
ValueError: Ordinal must be positive
# 
## ERROR: test_line_plot_period_frame (pandas.tseries.tests.test_plotting.TestTSPlot)

Traceback (most recent call last):
  File "C:\Users\candre4\pandas\pandas\tseries\tests\test_plotting.py", line 76, in test_line_plot_period_frame
    _check_plot_works(df.plot, df.index.freq)
  File "C:\Users\candre4\pandas\pandas\tseries\tests\test_plotting.py", line 118, in _check_plot_works
    plt.savefig(PNG_PATH)
  File "C:\Python27\lib\site-packages\matplotlib\pyplot.py", line 363, in savefig
    return fig.savefig(_args, *_kwargs)
  File "C:\Python27\lib\site-packages\matplotlib\figure.py", line 1084, in savefig
    self.canvas.print_figure(_args, *_kwargs)
  File "C:\Python27\lib\site-packages\matplotlib\backend_bases.py", line 1923, in print_figure
    *_kwargs)
  File "C:\Python27\lib\site-packages\matplotlib\backends\backend_agg.py", line 438, in print_png
    FigureCanvasAgg.draw(self)
  File "C:\Python27\lib\site-packages\matplotlib\backends\backend_agg.py", line 394, in draw
    self.figure.draw(self.renderer)
  File "C:\Python27\lib\site-packages\matplotlib\artist.py", line 55, in draw_wrapper
    draw(artist, renderer, *args, *_kwargs)
  File "C:\Python27\lib\site-packages\matplotlib\figure.py", line 798, in draw
    func(_args)
  File "C:\Python27\lib\site-packages\matplotlib\artist.py", line 55, in draw_wrapper
    draw(artist, renderer, *args, *_kwargs)
  File "C:\Python27\lib\site-packages\matplotlib\axes.py", line 1946, in draw
    a.draw(renderer)
  File "C:\Python27\lib\site-packages\matplotlib\artist.py", line 55, in draw_wrapper
    draw(artist, renderer, _args, *_kwargs)
  File "C:\Python27\lib\site-packages\matplotlib\axis.py", line 971, in draw
    tick_tups = [ t for t in self.iter_ticks()]
  File "C:\Python27\lib\site-packages\matplotlib\axis.py", line 907, in iter_ticks
    majorLabels = [self.major.formatter(val, i) for i, val in enumerate(majorLocs)]
  File "C:\Users\candre4\pandas\pandas\tseries\plotting.py", line 812, in __call__
    return Period(ordinal=int(x), freq=self.freq).strftime(fmt)
  File "C:\Users\candre4\pandas\pandas\tseries\period.py", line 101, in **init**
    raise ValueError("Ordinal must be positive")
ValueError: Ordinal must be positive
# 
## ERROR: test_line_plot_period_series (pandas.tseries.tests.test_plotting.TestTSPlot)

Traceback (most recent call last):
  File "C:\Users\candre4\pandas\pandas\tseries\tests\test_plotting.py", line 66, in test_line_plot_period_series
    _check_plot_works(s.plot, s.index.freq)
  File "C:\Users\candre4\pandas\pandas\tseries\tests\test_plotting.py", line 118, in _check_plot_works
    plt.savefig(PNG_PATH)
  File "C:\Python27\lib\site-packages\matplotlib\pyplot.py", line 363, in savefig
    return fig.savefig(_args, *_kwargs)
  File "C:\Python27\lib\site-packages\matplotlib\figure.py", line 1084, in savefig
    self.canvas.print_figure(_args, *_kwargs)
  File "C:\Python27\lib\site-packages\matplotlib\backend_bases.py", line 1923, in print_figure
    *_kwargs)
  File "C:\Python27\lib\site-packages\matplotlib\backends\backend_agg.py", line 438, in print_png
    FigureCanvasAgg.draw(self)
  File "C:\Python27\lib\site-packages\matplotlib\backends\backend_agg.py", line 394, in draw
    self.figure.draw(self.renderer)
  File "C:\Python27\lib\site-packages\matplotlib\artist.py", line 55, in draw_wrapper
    draw(artist, renderer, *args, *_kwargs)
  File "C:\Python27\lib\site-packages\matplotlib\figure.py", line 798, in draw
    func(_args)
  File "C:\Python27\lib\site-packages\matplotlib\artist.py", line 55, in draw_wrapper
    draw(artist, renderer, *args, *_kwargs)
  File "C:\Python27\lib\site-packages\matplotlib\axes.py", line 1946, in draw
    a.draw(renderer)
  File "C:\Python27\lib\site-packages\matplotlib\artist.py", line 55, in draw_wrapper
    draw(artist, renderer, _args, *_kwargs)
  File "C:\Python27\lib\site-packages\matplotlib\axis.py", line 971, in draw
    tick_tups = [ t for t in self.iter_ticks()]
  File "C:\Python27\lib\site-packages\matplotlib\axis.py", line 907, in iter_ticks
    majorLabels = [self.major.formatter(val, i) for i, val in enumerate(majorLocs)]
  File "C:\Users\candre4\pandas\pandas\tseries\plotting.py", line 812, in __call__
    return Period(ordinal=int(x), freq=self.freq).strftime(fmt)
  File "C:\Users\candre4\pandas\pandas\tseries\period.py", line 101, in **init**
    raise ValueError("Ordinal must be positive")
ValueError: Ordinal must be positive
# 
## ERROR: test_tsplot (pandas.tseries.tests.test_plotting.TestTSPlot)

Traceback (most recent call last):
  File "C:\Users\candre4\pandas\pandas\tseries\tests\test_plotting.py", line 59, in test_tsplot
    _check_plot_works(f, s.index.freq, ax=ax, series=s)
  File "C:\Users\candre4\pandas\pandas\tseries\tests\test_plotting.py", line 118, in _check_plot_works
    plt.savefig(PNG_PATH)
  File "C:\Python27\lib\site-packages\matplotlib\pyplot.py", line 363, in savefig
    return fig.savefig(_args, *_kwargs)
  File "C:\Python27\lib\site-packages\matplotlib\figure.py", line 1084, in savefig
    self.canvas.print_figure(_args, *_kwargs)
  File "C:\Python27\lib\site-packages\matplotlib\backend_bases.py", line 1923, in print_figure
    *_kwargs)
  File "C:\Python27\lib\site-packages\matplotlib\backends\backend_agg.py", line 438, in print_png
    FigureCanvasAgg.draw(self)
  File "C:\Python27\lib\site-packages\matplotlib\backends\backend_agg.py", line 394, in draw
    self.figure.draw(self.renderer)
  File "C:\Python27\lib\site-packages\matplotlib\artist.py", line 55, in draw_wrapper
    draw(artist, renderer, *args, *_kwargs)
  File "C:\Python27\lib\site-packages\matplotlib\figure.py", line 798, in draw
    func(_args)
  File "C:\Python27\lib\site-packages\matplotlib\artist.py", line 55, in draw_wrapper
    draw(artist, renderer, *args, *_kwargs)
  File "C:\Python27\lib\site-packages\matplotlib\axes.py", line 1946, in draw
    a.draw(renderer)
  File "C:\Python27\lib\site-packages\matplotlib\artist.py", line 55, in draw_wrapper
    draw(artist, renderer, _args, *_kwargs)
  File "C:\Python27\lib\site-packages\matplotlib\axis.py", line 971, in draw
    tick_tups = [ t for t in self.iter_ticks()]
  File "C:\Python27\lib\site-packages\matplotlib\axis.py", line 907, in iter_ticks
    majorLabels = [self.major.formatter(val, i) for i, val in enumerate(majorLocs)]
  File "C:\Users\candre4\pandas\pandas\tseries\plotting.py", line 812, in __call__
    return Period(ordinal=int(x), freq=self.freq).strftime(fmt)
  File "C:\Users\candre4\pandas\pandas\tseries\period.py", line 101, in **init**
    raise ValueError("Ordinal must be positive")
ValueError: Ordinal must be positive

---

Ran 1743 tests in 60.531s

FAILED (SKIP=10, errors=6)
