Verify that the main report and subreport are linked to the same export .MDB files.
  1. Go to the main report or design tab
  2. Select Report > Set Data Source Location
  3. In the "Current Data Source" box, you will see which .MDB file your report is linked to. The Report line shows you the .MDB file for the main report and the Subreport shows you the .MDB file for the subreport.
  4. If the two .MDB files do not match, reset the data source location