I believe multiple other sources were in error too but have since been corrected (including the online listing). I cannot prove this, however. But I do have an e-mail from my adviser indicating there was a change with the degree audit.Well, the school can certainly revoke a diploma based on an inadequacy on the transcript. The degree audit is a tool to determine if you've met all the requirements, but an error in the audit won't negate an inadequacy that it failed to catch. Although the audit may have been wrong, the school must have had a list of degree requirements posted, on a website or in a catalog, that is/was accessible to students. Even advisors make mistakes. The bottom line is that you are short one class and it's very doubtful that you'll be awarded a degree without it. It's unfortunate, and even unfair to a point, but I don't see any recourse.
http://www.usmh.usmd.edu/regents/bylaws/SectionIII/III250.html says that the university needs to develop, maintain, and publicize timely and accurate advising information to all students. http://registrar.umbc.edu/services/degree-audit/ says that the degree audit is an advisement tool (and importantly the ones students are to check for graduation). This whole situation doesn't seem timely or accurate.
I understand your point about no recourse. That is what I am exploring now. And I have a feeling you are right.
But if the degree audit had been correct, I would have taken the class and got everything squared away and not enrolled in my local community college and taken classes for the nursing program. (I probably would have endeavored for pharmacy school, though my grades might not have been good enough - then gone to accounting as a fall back if necessary).