Don't know what to tell you. I'm running out of solutions if you've tried everything else.

I do one other thing. It was bug that napster used to have (boy was that a long time ago). If you renamed a harddrive, or any of the folders that had files in them, the same thing would happen. To clarify, this bug would occur if any folder that contained any folder and so and so forth to your MP3s. What i'm trying to say is that for this bug if you changed the name of any of the folders that comprised the directory name of your shared folders (i.e. MacintoshHD/My Music/My Shared MP3s), Napster looked for the old save or share directory and couldn't find it, stalling all operations. The solution was just to go to the preferences and rename the shared and saved folder to the folders you want.

I can't believe this works, but it's worth a shot.