Structures are out of sync from the data.
This might occur if you have altered the MDB file with MS Access. For example, if you edit the MOL_ID field or recreate it in the Moltable, this will make the structures go out of sync with the data.
Also, one of the features that MS Access gives you is the ability to "Compact and Repair the Database". When you do this compacting and repairing, structures will go out of synch with the data.
You can try exporting the database as an SD File and reimporting it, but if that does not help, the only option will be to revert back to a back up of the database before the MDB file was modified.