error en glmmadmb

Dear list,

after checking for collinearity, overdispersion and zeroinflation of  
my data I found the glmmadmb the best approach for them.


So, I'm now starting from the following code:


Model<-glmmadmb(Cor.affi~Depth+Temp+pH+Sal+TN+TP+Tur+Chla+Fish+fType+Sub_Veg+(1|fPonds)+(1|fYear:fDate),data=na.omit(dataLG1),
family="nbinom",zeroInflation=TRUE)

Number of observations:  total=239, fPonds=42, fYear:fDate=8


to find the best fixed structure through the backward  
elimination,however when I ran this model:


M9<-glmmadmb(Cor.affi~  
Depth+TP+Tur+fType+Sub_Veg+(1|fPonds)+(1|fYear:fDate),data=na.omit(dataLG1),
family="nbinom",zeroInflation=TRUE)

I get the following error:

Parameters were estimated, but not standard errors were not: the most  
likely problem is that the curvature at MLE was zero or negative
Error in glmmadmb(Cor.affi ~ Depth + TP + Tur + fType + Sub_Veg + (1 |  :
  The function maximizer failed (couldn't find STD file)  
Troubleshooting steps include (1) run with 'save.dir' set and inspect  
output files; (2) change run parameters: see '?admbControl'
In addition: Warning message:
running command './glmmadmb -maxfn 500 -maxph 5 -noinit -shess' had status 1

that only appears at this stage by removing the variable Fish (P/A).

Could anyone give me any suggestion?

Thank in advance