At ArcGIS 10, the geodatabase system table schema was significantly changed, the set of GDB_* tables have been consolidated into a smaller collection of tables. As part of this consolidation, the mechanism used by older clients to determine whether an Access database was a Geodatabase has been changed. This change has an adverse effect in that older clients are now recognizing ArcGIS 10 personal geodatabases as simply an Access database.
While older clients can connect to ArcGIS 10 personal geodatabases, they cannot view or update any of the geodatabase content. The creation of datasets is also prevented.
ArcGIS 9.3.1 SP2 contains an updated mechanism to raise the appropriate error, upon connection to an ArcGIS 10 personal geodatabase.