I get emails every now and then about iTunesDSM getting stuck in the unknown artist or unknown album. It seems to be that Java sometimes has an issue with hidden files or folders on the Operating System and iTunes seems to carry over some of those files or folders into the unknown artist/unknown album folder. Here are somethings you can try:
1. Temporarily remove the unknown artist or unknown album from the music directory and run the scan on the music directory. Then replace the folder.
2. Scan each folder inside the unknown artist or unknown album individually, searching for the offending folder.
Hopefully this helps - there is currently no way to fix this issue. It might be once Java 1.7 is released there may be a better way to handle this though.