title: H5py IOError: Can't write data
body: <p>For a deep learning project, I reorganize data from hdf5 files into a big training_data.hfd5 containing batch0...batch_max
  When running it in local on my laptop it works, but the process is a bit long (much data), so I tried to run it on big-CPU servers I have access to.
  Now I have this error :</p>
  
  <pre><code>Traceback (most recent call last):
    File "prepare_data.py", line 88, in &lt;module&gt;
      main(readargs())
    File "prepare_data.py", line 82, in main
      prepare_data('', args)
    File "prepare_data.py", line 72, in prepare_data
      args.preprocessdatadir, args.datadir, stdout=None)
    File "/home/bizeul/Stage/GCNN-1/GCNN_Icube/data_prepare_cube/group_batch.py", line 113, in group_batchs
      curr_batch_idx, count_events = organizer.iter_data()
    File "/home/bizeul/Stage/GCNN-1/GCNN_Icube/data_prepare_cube/group_batch.py", line 93, in iter_data
      self.next_batch(batchsize)
    File "/home/bizeul/Stage/GCNN-1/GCNN_Icube/data_prepare_cube/group_batch.py", line 65, in next_batch
      self.next_event(fileout)
    File "/home/bizeul/Stage/GCNN-1/GCNN_Icube/data_prepare_cube/group_batch.py", line 82, in next_event
      fileout[self.group_name + '/label'][self.event_idx] = label
    File "h5py/_objects.pyx", line 54, in h5py._objects.with_phil.wrapper (/home/bizeul/virtual_cpu/build/h5py/h5py/_objects.c:2840)
    File "h5py/_objects.pyx", line 55, in h5py._objects.with_phil.wrapper (/home/bizeul/virtual_cpu/build/h5py/h5py/_objects.c:2798)
    File "/home/bizeul/virtual_cpu/lib/python2.7/site-packages/h5py/_hl/dataset.py", line 630, in __setitem__
      self.id.write(mspace, fspace, val, mtype, dxpl=self._dxpl)
    File "h5py/_objects.pyx", line 54, in h5py._objects.with_phil.wrapper (/home/bizeul/virtual_cpu/build/h5py/h5py/_objects.c:2840)
    File "h5py/_objects.pyx", line 55, in h5py._objects.with_phil.wrapper (/home/bizeul/virtual_cpu/build/h5py/h5py/_objects.c:2798)
    File "h5py/h5d.pyx", line 221, in h5py.h5d.DatasetID.write (/home/bizeul/virtual_cpu/build/h5py/h5py/h5d.c:3680)
    File "h5py/_proxy.pyx", line 132, in h5py._proxy.dset_rw (/home/bizeul/virtual_cpu/build/h5py/h5py/_proxy.c:2022)
    File "h5py/_proxy.pyx", line 93, in h5py._proxy.H5PY_H5Dwrite (/home/bizeul/virtual_cpu/build/h5py/h5py/_proxy.c:1732)
  IOError: Can't write data (No appropriate function for conversion path)
  </code></pre>
  
  <p>What do you think is the problem ?</p>