This issue arises because Crystal Reports XI locks the exported database file (.MDB) when the report is previewed in the application. Once the Crystal Reports XI application is closed then the database is automatically unlocked. This can be inconvenient when quick updates to the export file is needed. Using the Log Off Server feature in Crystal Reports XI will allow the database to be unlocked while both the application and the report remains open.
Follow these steps with the report open in Crystal Reports XI:
Click on Database, Log On or Off Server (a Data Explorer window will pop up with the MDB file highlighted)