This message indicates that your data source is an Access database, and that Server can't open it. The message itself is generated by Microsoft and is somewhat misleading. There are a number of different reasons why the JET engine might not be able to open the database beyond the fact that someone else has it open...it would be a pretty long message if it told you ALL the stuff to check for, though
Most often, the reason is that the Active Directory "Run As" account that you are running Tableau Server under doesn't have access to the file share in which the database is sitting. SO, when JET tries to open the database, it fails, and the "not quite right" error message is thrown.
Hope this helps!