If you recieve an error message while attempting to upgrade an Access database from 5.0 to 5.1, the most likely cause is a corrupt database.  To repair an Access database follow these steps:

1. Start Microsoft Access

2. Select Tools->Database Utilities->Compact and Repair Database

3. Locate the corrupt database and click the Compact button

4. Type in a new name for your database and click Save.

Geotab recommends that after the database is repaired, that you upgrade from Access to SQL Server.  For instructions on how to upgrade from Access to SQL please view the following post:

http://www.geotab.com/Support/GeotabForum/tabid/108/forumid/2/threadid/19/scope/posts/Default.aspx