Microsoft Access Sharing

I have 3 Users that need to use the same databae in 3 different offices. 2 with full control and 1 read only. (sounds easy enough) I have a MS Access database in 2003 server (LAN).I have shared the folder where the Database resides and given permissions to each user(Active directory) set permissons to the shared folder. I have mapped this drive to all the work group computers. I have created shortcut from this mapped drive to all clients. This works fine for a while then randomly could be a day a week..changes all 3 users to read only permissions. I even tried setting all permissions to full control to the shared directory and and using the /ro(read only)command line switch and placed the shortcut on the 1 users desktop I get the same results. Any other suggestions thanks