[R-sig-ME] CHOLMOD warning with GLMM

[Renwick, A. R.]

Dear All
I am trying to model the burden of fleas on field voles using a GLMM with poisson error and a nested random effect.
The random effect is (1|Farm/Margin) I have 7 farms and 14 margins (2 margins per farm) and have sampled each margin 4 times.
However, I continually get an error message even when I simplify the model.  The model I am trying to run is:


bin<-lmer(fleaburden ~ sex + width + month + vole abundance + alternative host abunandance +(1|Farm/Margin), family=poisson, data=flea, REML=FALSE)


The error message:

CHOLMOD warning: ‡e

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

Any help in understanding this error would be much appreciated.

Thanks,
Anna

Anna Renwick
Institute of Biological & Environment Sciences
University of Aberdeen
Zoology Building
Tillydrone Avenue
Aberdeen
AB24 2TZ


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