R help - Oct 2005 - Missing Data?

I am using glmmPQL on a dataset which has no missing values:

antgl<-glmmPQL(SF~Proc*Min, random= ~1|Trial, family="binomial")

I get the error message:

iteration 1
Error in na.fail.default(list(invwt = c(1.36892171002990, 1.36680104392581,  
:
        missing values in object

I also get this error if na.action is set na.fail. If I set na.action to 
na.omit to ignore the (mythical) missing values, I get other error messages.

There are no missing values - I have used is.na(antgl) to check this. Can 
anyone explain why it seems to think there are?

Thanks