[R-sig-ME] lme4 and false convergence

[Ben Zuckerberg]

Dear R-users,

I am using the most updated package of lme4 (lme4_0.999375-2).  I have a 
data set consisting of ~900 observations at ~440 independent survey 
sites.  There are an unbalanced number of surveys at each site.  I am 
attempting to develop several models evaluating the presence/absence of 
a species (PRES) at these random sites (SITE) using a number of 
predictor variables.  The response variable (PRES) is binomial and the 
included predictor variables are either proportions (e.g., AG, FOR, 
OPEN, LDEV,or DEV) or numerical (COUNT[min. 1 to max. 37,mean = 10]). 
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PROBLEM 1:

I have developed the following GLMM:

mix.1<-glmer(PRES~AG+FOR+OPEN+LDEV+DEV+COUNT+(1|SITE),family=binomial,data=merge1) 


I receive the following error:
Warning message:
In mer_finalize(ans) : false convergence (8)

There is model output, but I am worried it might be biased.
I have tried:
-Data transformation of the predictor variables (e.g., log(COUNT)), 
which does seem successful in some simpler models, but does not work 
consistently.
-The most updated version of lme4

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PROBLEM #2:
In addition, I am interested in visualizing the predicted probabilities 
from this output using the fixed effect function, but receive the 
following message:

fixef(mix.1)
Error in UseMethod("fixef") : no applicable method for "fixef"

Any suggestions would be greatly appreciated!

-- 
Benjamin Zuckerberg, Ph.D.
Post-doctoral Associate
Spatial Ecologist, Citizen Science
Cornell Laboratory of Ornithology
159 Sapsucker Woods Road
Ithaca, NY 14850 
Tele: 607-254-2174
Fax: 607-254-2111