1. You opened the mdb file and edited/saved/converted it to a newer format unrecognized by Clay. You have to save it as the original Access 2000 format.
2. The mdb file got corrupted due to a machine crash. Try closing Outlook, opening the mdb file in Access and see if it asks you whether to attempt a repair. Or run Compact and Repair in Access for a manual repair.
Exit Outloook, rename the bad file, then reload Outlook and relogin/synchronize. This will rebuild the offline database. But keep in mind two things:
1. If you had any items offline that weren't synchronized with Central, these will be lost.
2. First time synchronization by default only synchronizes active items. You may want to manually synchronize some tables for which you need inactive items, especially the Tasks table (in case you want to change or track Outlook closed Appointments/Tasks). To do this, go to Clay Outlook's toolbar, select Tools/Synchronize, and select the table and a date that goes far back enough for you.
same administrator and same passowrd and it works.