Using ADDUSERS.EXE from the resource kit, you can remove these unusable entries:
1. Run ADDUSERS /D USERLIST.TXT to dump the user and group information to the USERLIST.TXT file.
2. Edit the USERLIST.TXT file so that it only contains the invalid data and their section headers (text in square brackets).
3. Run ADDUSERS /E USERLIST.TXT to erase the bad relationships and groups.
NOTE: Later service packs will prevent group names in excess of 20 character from being created.