[R] NA values in Standard Error for zeroinfl()

[Chris Fowler]

I am fitting a model using zeroinfl() and it runs without errors, 
returning results that are generally consistent with my hypotheses.

One of my variables is percent black (pblack). This variable was highly 
significant in some of the other count models I ran on the way to my 
current formulation. It is not significant in this model. As such I 
decided to try adding pblack^2 to the model to see whether the issue 
might captured there (if it matters I created a new variable in my data 
frame called pblacksqared and added that to the count portion of the 
model only).

zeroinfl() runs just fine and pblack becomes significant and moves in 
the appropriate direction once the new variable is added to the model. 
However, pblacksquared is not significant, and while a coefficient is 
generated, I get NA values for Std. Error, z value and Pr(>|z|). pblack 
and pblacksquared are both positive and continuous with no missing values.

I can't find anything in the documentation about returning an NA value 
here. Any suggestions as to where it comes from and how I might 
interpret/remedy it?

Thanks,

Chris