I'm in my last semester of grad school, and I had to get permission for thesis for 6 credits. I submitted everything within deadline. I got an email that same day that someone in the grad office entered in only 1 credit, not 6, that they withdrew me from the class and I would be added after add/drop. They went to fix it and two weeks later I was enrolled (approved for late add). I just found out that I owe $1000 or I will be dropped from my classes and financial aid took away my previously approved loan without seeing if I was still in enrollment (they assumed I was still part time after checking before the late add). I talked to them, and hopefully they will fix it, but if they don't, I will lose my degree and money to help me get by (TA job and loan) due to something out of my control.
If the schools negligence in handling your credits and loan are the reason you lost the loan, then you may have a claim against the university. However, I would try to work it out with them and ask them to credit the amount you owe. It is likely they will want to avoid legal fees for such a small amount.