Why do I get this message -"We won't be able to E-file your return" when I did not e-file PA return as software seems to think. Why can't I re-file Federal return?

Software says "Why? Well, it looks like you have a tax situation in the Pennsylvania return that makes it ineligible for e-filing - return is an amended return."  I did not e-file my PA taxes yet, only Federal (I plan on mailing PA return).  Why would this prevent me from e-filing an amended Federal return?