Try closing Essential Forms and rebooting the computer. Launch Essential forms. Do you still get the error?

Try To Pack And Reindex The Database:

With everyone out of the Essential Forms program (if it's on a network), to pack and reindex the database go ahead and open the program on one workstation. In the program up on the menu bar click on Configure>Preferences>Database and check both "Pack databases on program launch" and "Reindex databases on program launch", Click "Ok". and close and reopen the program once in that mode. Then, go back in and UNcheck those two boxes in Configure>Preferences>Database and uncheck both: "Pack databases on program launch" and "Reindex databases on program launch, " then click "Ok". That’s it!

If everybody's networked to the same database, only one user needs to successfully perform the pack and reindex in order to fix the problem.