Try installing MC12 and see if it won't convert your library.
For the record, I installed MC12 (build 147), and used it to Open my MC10 library, and it converted it flawlessly. The upgrade was seamless. In fact, I can run MC10 and MC12 side-by-side on the same machine (which has proven useful for replicating some of my settings). You just need to point them at different library directories, since MC10 can't read an MC12 library (I don't think - didn't actually try that).
The only thing that could have been better is automatically preserving some of the config options (like Gapless seeks, thresholds for breaking tracks in Sound Recorder, etc). But, I'm not complaining - that is very minor consequence of a major version upgrade.
Soundman.
