Well, I hope you have a backup of the workgroup file (*.mdw) cause you're going to need it. I had a similar problem recently where the workgroup file had somehow been corrupted. Replaced with my backup and no problems.
No backup? Check with your IT guys to see if they can pull off a backup restore from the mainframe of the workgroup file.
Don't have that? Man are you screwed. Well, maybe not. You are going to have to get by the security somehow though. Do some searches on "removing security" and you should find some useful information.
Good luck.