As an update - I tried testing the model as follows:
1) Including Group+Sex (taking out MEdu) - This still failed (same error message).
2) Including Group+MEdu (taking out Sex) - This is working!
I think it might be because when I include Sex and MEdu as additional factors, the contingency tables look like this:
Contingency tables of subject distributions among the categorical variables:
, , MEdu = 2
Sex
Group Female Male
HR 7 12
LR 0 3
, , MEdu = 3
Sex
Group Female Male
HR 9 14
LR 3 8
, , MEdu = 4
Sex
Group Female Male
HR 5 14
LR 6 6
where among subjects who have MEdu=2, there are no female LR subjects. Is there a way to still include Sex as a factor without the program erroring out?
As a side note, I am interested in the main effect of Group and am including Sex and MEdu as covariates of no interest.
Thanks!
Janelle