title: Error when Fitting a glmer with poisson error structure
body: <p>I hope somebody can help me. I'm trying to conduct an analysis which examines the number of samples of Hymenoptera caught over an elevational gradient. I want to examine the possibility of a uni-modal distribution in relation to elevation, as well as a linear distribution. Hence I am including <code>I(Altitude^2)</code> as an explanatory variable in the analysis.</p>
  
  <p>I am trying to run the following model which includes a Poisson error structure (as we are dealing with count data) and date and Trap Type (<code>Trap</code>) as random effects.</p>
  
  <pre><code>model7 &lt;- glmer(No.Specimens~Altitude+I(Altitude^2)+(1|Date)+(1|Trap),
         family="poisson",data=Santa.Lucia,na.action=na.omit)
  </code></pre>
  
  <p>However I keep receiving the following error message:</p>
  
  <pre><code>Error: (maxstephalfit) PIRLS step-halvings failed to reduce deviance in pwrssUpdate
  In addition: Warning messages:
  1: Some predictor variables are on very different scales: consider rescaling 
  2: In pwrssUpdate(pp, resp, tolPwrss, GQmat, compDev, fac, verbose) :
    Cholmod warning 'not positive definite' at file:../Cholesky/t_cholmod_rowfac.c, line 431
  3: In pwrssUpdate(pp, resp, tolPwrss, GQmat, compDev, fac, verbose) :
    Cholmod warning 'not positive definite' at file:../Cholesky/t_cholmod_rowfac.c, line 431
  </code></pre>
  
  <p>Clearly I am making some big mistakes. Can anybody help me figure out where I am going wrong? </p>
  
  <p>Here is the structure of the dataframe:</p>
  
  <pre><code>str(Santa.Lucia)
  'data.frame':   97 obs. of  6 variables:
   $ Date        : Factor w/ 8 levels "01-Sep-2014",..: 6 6 6 6 6 6 6 6 6 6 ...
   $ Trap.No     : Factor w/ 85 levels "N1","N10","N11",..: 23 48 51 14 17 20 24 27 30 33 ...
   $ Altitude    : int  1558 1635 1703 1771 1840 1929 1990 2047 2112 2193 ...
   $ Trail       : Factor w/ 3 levels "Cascadas","Limones",..: 1 1 1 1 1 3 3 3 3 3 ...
   $ No.Specimens: int  1 0 2 2 3 4 5 0 1 1 ...
   $ Trap        : Factor w/ 2 levels "Net","Pan": 2 2 2 2 2 2 2 2 2 2 ...
  </code></pre>
  
  <p>And here is the complete data.set (these are only my preliminary analyses)</p>
  
  <pre><code>           Date Trap.No Altitude    Trail No.Specimens Trap
  1   28-Aug-2014      W2     1558 Cascadas            1  Pan
  2   28-Aug-2014      W5     1635 Cascadas            0  Pan
  3   28-Aug-2014      W8     1703 Cascadas            2  Pan
  4   28-Aug-2014     W11     1771 Cascadas            2  Pan
  5   28-Aug-2014     W14     1840 Cascadas            3  Pan
  6   28-Aug-2014     W17     1929    Tower            4  Pan
  7   28-Aug-2014     W20     1990    Tower            5  Pan
  8   28-Aug-2014     W23     2047    Tower            0  Pan
  9   28-Aug-2014     W26     2112    Tower            1  Pan
  10  28-Aug-2014     W29     2193    Tower            1  Pan
  11  28-Aug-2014     W32     2255    Tower            0  Pan
  12  30-Aug-2014      N1     1562 Cascadas            5  Net
  13  30-Aug-2014      N2     1635 Cascadas            0  Net
  14  30-Aug-2014      N3     1723 Cascadas            2  Net
  15  30-Aug-2014      N4     1779 Cascadas            0  Net
  16  30-Aug-2014      N5     1842 Cascadas            3  Net
  17  30-Aug-2014      N6     1924    Tower            2  Net
  18  30-Aug-2014      N7     1979    Tower            2  Net
  19  30-Aug-2014      N8     2046    Tower            0  Net
  20  30-Aug-2014      N9     2110    Tower            0  Net
  21  30-Aug-2014     N10     2185    Tower            0  Net
  22  30-Aug-2014     N11     2241    Tower            0  Net
  23  31-Aug-2014      N1     1562 Cascadas            1  Net
  24  31-Aug-2014      N2     1635 Cascadas            1  Net
  25  31-Aug-2014      N3     1723 Cascadas            0  Net
  26  31-Aug-2014      N4     1779 Cascadas            0  Net
  27  31-Aug-2014      N5     1842 Cascadas            0  Net
  28  31-Aug-2014      N6     1924    Tower            0  Net
  29  31-Aug-2014      N7     1979    Tower            7  Net
  30  31-Aug-2014      N8     2046    Tower            4  Net
  31  31-Aug-2014      N9     2110    Tower            6  Net
  32  31-Aug-2014     N10     2185    Tower            1  Net
  33  31-Aug-2014     N11     2241    Tower            1  Net
  34  01-Sep-2014      W1     1539 Cascadas            0  Pan
  35  01-Sep-2014      W2     1558 Cascadas            0  Pan
  36  01-Sep-2014      W3     1585 Cascadas            2  Pan
  37  01-Sep-2014      W4     1604 Cascadas            0  Pan
  38  01-Sep-2014      W5     1623 Cascadas            1  Pan
  39  01-Sep-2014      W6     1666 Cascadas            4  Pan
  40  01-Sep-2014      W7     1699 Cascadas            0  Pan
  41  01-Sep-2014      W8     1703 Cascadas            0  Pan
  42  01-Sep-2014      W9     1746 Cascadas            1  Pan
  43  01-Sep-2014     W10     1762 Cascadas            0  Pan
  44  01-Sep-2014     W11     1771 Cascadas            0  Pan
  45  01-Sep-2014     W12     1796 Cascadas            1  Pan
  46  01-Sep-2014     W13     1825 Cascadas            0  Pan
  47  01-Sep-2014     W14     1840    Tower            4  Pan
  48  01-Sep-2014     W15     1859    Tower            2  Pan
  49  01-Sep-2014     W16     1889    Tower            2  Pan
  50  01-Sep-2014     W17     1929    Tower            0  Pan
  51  01-Sep-2014     W18     1956    Tower            0  Pan
  52  01-Sep-2014     W19     1990    Tower            1  Pan
  53  01-Sep-2014     W20     2002    Tower            3  Pan
  54  01-Sep-2014     W21     2023    Tower            2  Pan
  55  01-Sep-2014     W22     2047    Tower            0  Pan
  56  01-Sep-2014     W23     2068    Tower            1  Pan
  57  01-Sep-2014     W24     2084    Tower            0  Pan
  58  01-Sep-2014     W25     2112    Tower            1  Pan
  59  01-Sep-2014     W26     2136    Tower            0  Pan
  60  01-Sep-2014     W27     2150    Tower            1  Pan
  61  01-Sep-2014     W28     2193    Tower            1  Pan
  62  01-Sep-2014     W29     2219    Tower            0  Pan
  63  01-Sep-2014     W30     2227    Tower            1  Pan
  64  01-Sep-2014     W31     2255    Tower            0  Pan
  85   03/06/2015    WT47     1901    Tower            2  Pan
  86   03/06/2015    WT48     1938    Tower            2  Pan
  87   03/06/2015    WT49     1963    Tower            2  Pan
  88   03/06/2015    WT50     1986    Tower            0  Pan
  89   03/06/2015    WT51     2012    Tower            9  Pan
  90   03/06/2015    WT52     2033    Tower            0  Pan
  91   03/06/2015    WT53     2050    Tower            4  Pan
  92   03/06/2015    WT54     2081    Tower            2  Pan
  93   03/06/2015    WT55     2107    Tower            1  Pan
  94   03/06/2015    WT56     2128    Tower            4  Pan
  95   03/06/2015    WT57     2155    Tower            0  Pan
  96   03/06/2015    WT58     2179    Tower            2  Pan
  97   03/06/2015    WT59     2214    Tower            0  Pan
  98   03/06/2015    WT60     2233    Tower            0  Pan
  99   03/06/2015    WT61     2261    Tower            0  Pan
  100  03/06/2015    WT62     2278    Tower            0  Pan
  101  03/06/2015    WT63     2300    Tower            0  Pan
  102  04/06/2015    WT31     1497 Cascadas            0  Pan
  103  04/06/2015    WT32     1544 Cascadas            1  Pan
  104  04/06/2015    WT33     1568 Cascadas            1  Pan
  105  04/06/2015    WT34     1574 Cascadas            0  Pan
  106  04/06/2015    WT35     1608 Cascadas            5  Pan
  107  04/06/2015    WT36     1630 Cascadas            3  Pan
  108  04/06/2015    WT37     1642 Cascadas            0  Pan
  109  04/06/2015    WT38     1672 Cascadas            5  Pan
  110  04/06/2015    WT39     1685 Cascadas            6  Pan
  111  04/06/2015    WT40     1723 Cascadas            3  Pan
  112  04/06/2015    WT41     1744 Cascadas            2  Pan
  113  04/06/2015    WT42     1781 Cascadas            1  Pan
  114  04/06/2015    WT43     1794 Cascadas            2  Pan
  115  04/06/2015    WT44     1833 Cascadas            0  Pan
  116  04/06/2015    WT45     1855 Cascadas            4  Pan
  117  04/06/2015    WT46     1876 Cascadas            2  Pan           
  </code></pre>