[R] Error fitting ZIP with zeroinfl()

[Paige Barlow]

I am attempting to fit a full zero-inflated Poisson model then use 
backward elimination to arrive at the best-fitting model.  When I try to 
fit the model with zeroinfl() I get this error:

Error in while (abs((ll_old - ll_new)/ll_old) > control$reltol) { :
        missing value where TRUE/FALSE needed

Any suggestions?

Thanks for your help!

Paige Barlow
MS Student
Virginia Tech
Dept Fish and Wildlife