Can someone run commands in startup-sequence/user-startup and WBStartup manually until system crashes? This bug must be found quickly.
New filesystem code has one big difference, old code handled "illegal" filenames very differently than new. Old simply failed to open file if filename was "illegal", new supports all "illegal" filenames (it stores "illegal" filenames in a special file _UAEFSDB.___) but code that detects when file name is "illegal" is different. This may cause problems with "semi-illegal" filenames.
I guess some program that gets run when system starts stores config data in a file that has "semi-illegal" name (new filesystem code tries to read it from _UAEFSDB.___ = file not found)