[R] lmer with spatial and temporal random factors, not nested

[Marte Lilleeng]

Hi, I am new to this list.
I have a question regarding including both spatial and temporal random
factors in lmer. These two are not nested, and an example of model I
try to fit is

model1<-lmer(Richness~Y+Canopy+Veg_cm+Treatment+(1|Site/Block/Plot)+(1|Year),
family=poisson, REML=FALSE),
where
richness = integer
Y & Treatment = factor
Canopy & Veg_cm = numerical, continous
Site/Block/Plot= factor
Year = integer

I get the following warning message:

Warning messages:
1: In mer_finalize(ans) :
  Cholmod warning 'not positive definite' at
file:../Cholesky/t_cholmod_rowfac.c, line 432
2: In mer_finalize(ans) : singular convergence (7)

Is this due to the nature of my fixed/random factors or the way I put
up the random factors?

In lme I could include a component for autocorrelation,
ex:cor=corAR1(form=~Year|Site/Block/ID). Does the equivalent exist for
lmer?

I will be very happy if someone can help me!


-- 
Thanks a lot

Marte