Error en mer_finalize(ans) : Downdated X'X is not positive definite, 1. What is wrong with my model?

Dear List Members,

I am trying to run the following model in glmer:

M_bud_type1=glmer(Dead~Treatment* fBud_type + fBud_type:Species +  
(1|fRep), family=binomial, data=species)

where:
- Dead is a binomial response variable
- fBud_type is a fixed factor with 3 levels
- Species is a fixed factor with 9 levels nested within fBud_type and
- fRep is a random factor with 27 levels nested within Species

I have 1386 observations.
The error message I receive reads:

Error en mer_finalize(ans) : Downdated X'X is not positive definite, 1.

Any suggestions as to what can be wrong?

Thanks for your help,

Cheers!

Sara