If any of the references are broken, you'll run into problems even if the
function in question isn't in the library whose reference is broken. That's
because Access tries to search through all of the referenced libraries in
its search, and can't handle when there's a problem.

For far more than you could ever want to know about this problem, check out
http://members.rogers.com/douglas.j.steele/AccessReferenceErrors.html