I have a relatively complicated Excel application with maybe 30 routines and 100's of lines of VBA code. During development over the past several months, I diligently saved different versions, and frequently save while making modifications. After my last modification (can't be 100% sure but I think I just renamed a routine), Excel now hangs when trying to open the workbook. If I disable macros I can open it, but the moment I enable macros, Excel hangs (can't even kill it via task manager End Task). CPU is at 25% so it doesn't appear to be an infinite loop. I can open other worbooks with macros without issue.

Any suggestion as to how I can go about diagnosing and fixing the issue? I can certainly resume from my last version and lose about 4 hours of work, but I'd like to see if I can figure out what is wrong. Whatever the issue is might also be in previous versions.