Greg, a lot of students don't understand how the financial aid process works, so I'll highlight it for you in case you don't know (or to help others reading this post). Every year you filled out a FAFSA, right? Well, the school takes that information, develops an EFC ("Expected Family Contribution") and then awards aid. You probably received an Award Letter, which details what aid was offered, then you had to sign and accept some or all of it. Depending on the college's rules (and the type of aid you accepted) you may have to meet cerain enrollment qualifications - typically full time enrollment. So if you dropped a class that last semester you attended, that could have reduced the aid you were awarded, and your account was corrected retroactively.
Without seeing your aid information, I can't really offer more specific advice. But again, I would ask for a semester-by-semester breakdown of your account. Find the point where you were paid up and start there. Have them explain to you why you owe the money.
Honestly, your best bet is to finish your degree there since it's highly unlikely your credits will transfer in bulk. If you start again at another school you could end up needing an additional two years or so. It's just not worth it.
And no, I don't work for AIU! I work for a private college and have a lot of experience with this. I don't generally recommend for-profit schools, but with only a semester to go, it's your best bet.