title: Error: Invalid grouping factor specification
body: <p>I am trying to use <code>glmer</code> to model coral recruitment and get the error "Error: Invalid grouping factor specification, Site" when I run the model after re-scaling the variables. Help greatly appreciated</p>
  
  <pre><code>m1&lt;-glmer(Tot~cs.Tile(Tile)+cs.Coral_T(Coral_T)+cs.Sponge(Sponge)+
  cs.Turf(Turf)+cs.Acro(Acro)+cs.Por(Por)+cs.Poc(Poc)+
  cs.Mer(Mer)+cs.Agar(Agar)+cs.Fav(Fav)+
  cs.Den(Den)+cs.Sid(Sid)+cs.CCA(CCA)+cs.Soft(Soft)+
    (1|Site), 
  family=poisson, data=data)
  </code></pre>
  
  <p>I have 16 variables and 368 obs:</p>
  
  <pre><code>str(data)
  'data.frame':   368 obs. of  16 variables:
   $ Site   : Factor w/ 25 levels "Eight","Eighteen",..: 10 10 10 10 10 10 10 10 10 10 ...
   $ Tile   : int  1 2 3 4 5 6 7 8 9 10 ...
   $ Tot    : int  28 24 17 13 29 19 6 13 14 4 ...
   $ Coral_T: num  32.6 32.6 32.6 32.6 32.6 ...
   $ Sponge : num  0.206 0.206 0.206 0.206 0.206 ...
   $ Turf   : num  32.3 32.3 32.3 32.3 32.3 ...
   $ Acro   : num  3.45 3.45 3.45 3.45 3.45 ...
   $ Por    : num  1.15 1.15 1.15 1.15 1.15 ...
   $ Poc    : num  0 0 0 0 0 0 0 0 0 0 ...
   $ Mer    : num  0.175 0.175 0.175 0.175 0.175 0.175 0.175 0.175 0.175 0.175 ...
   $ Agar   : num  24.2 24.2 24.2 24.2 24.2 ...
   $ Fav    : num  1.02 1.02 1.02 1.02 1.02 ...
   $ Den    : num  1.18 1.18 1.18 1.18 1.18 ...
   $ Sid    : int  0 0 0 0 0 0 0 0 0 0 ...
   $ CCA    : num  0.07 0.07 0.07 0.07 0.07 0.07 0.07 0.07 0.07 0.07 ...
   $ Soft   : num  0 0 0 0 0 0 0 0 0 0 ...
  </code></pre>