This happened to me last month and I posted about it here. For me it was that I had a file that MC did not recognize somewhere in my library. No amount of backup, or building a new library helped because MC would just freeze on this particular file every time it scanned the library on startup. I have 2 terrabytes of FLAC files alone so I wasen't going to go thry every file just yet. Instead I went into the Options menu and under AUDIO file types I only checked the files that I know are in my library for playback -specifically FLAC, WMA, AAC, DFF, MP3. The rest I left unchecked. Now when I start up MC, and MC scans my library, it ignaores all files other than these, and thus it stopped crashing. I can't say this will solve your issue but you should have checked only the files you use anyway.
Hope this helps.
Jimmy