[R] Multiple CHOLMOD errors when attempting poisson glmm

[postava-davig.m]

Hello,

I have been attempting to run a poisson glmm using lme4 for some time now
and have had a lot of trouble.  I would say 9 times out of 10 I receive the
following warning:

CHOLMOD warning: %h
Error in mer_finalize(ans) : 
  Cholmod error `not positive definite' at
file:../Cholesky/t_cholmod_rowfac.c, line 432

My data are counts of microbe colony forming units (CFUs) collected from
termite cuticles and the surrounding environment over a 3 year period.  I am
attempting to analyze the effect of several factors on these counts (termite
nest volume, temperature, humidity, light, incubation temperature, habitat,
year, sample location, etc.) to determine which account for the variance in
microbial communities.  These data are observations, so there are many
missing values....which may be part of the problem.  I've tried many
different combinations of variables, and also have tried reducing my data
set to remove as many NA's and confounding variables as possible, but I
still can't get any models to work consistently.  One most recent attempt
had the following output:

model1=lmer(totalcfus~habitat*temp*moisture*light+location+(1|habitat/colony/location),family=poisson,control=list(msVerbose=1))
  0:     553377.59:  1.00573 0.620530 0.169516  26.3904 -13.1266 -33.2286
-21.1955 -21.1064 -0.590761 -0.217403 -0.0342272 -0.960593 -0.0962517
0.441626  1.20575 0.718621 0.680580 0.171006 0.403729 0.278822 0.275395
0.00707767 0.0225599 0.0854869 0.0533373 0.0243451 0.00114120 0.000403226
-0.00566960 -0.0143715 -0.00931896 -0.00879323 -0.000753236 -0.00335745
-0.00178054 -0.000788027 -0.000288944 -0.000909455 -0.000839295 -0.000309293
-1.35885e-05 9.76120e-06 3.57035e-05 2.78985e-05 1.01880e-05
CHOLMOD warning: %h
Error in mer_finalize(ans) : 
  Cholmod error `not positive definite' at
file:../Cholesky/t_cholmod_rowfac.c, line 432

I have to admit that I'm at a loss, and have been unable to determine any
pattern to when this error message comes up.  I'm hoping that someone can
help me eek out what the issue is with my data so that I can eventually work
out a usable model.

Thanks so much, and happy holidays.
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