This error message will appear if a calculation is performed on a table, while editing, in a personal geodatabase with more than 9,500 records:
Lock Count Exceeded
The Editor uses the Microsoft Jet Engine, which has a lock count of 9,500 records by default.
You may increase the lock count by altering the lock count setting in the Editor tab of the ArcMap Advanced Settings Utility.
This setting is used to protect database server resources; thus, increasing it could cause server performance problems. Contact your system administrator prior to changing this setting.