Adprep was unable to verify whether operation %1 has completed. Status/Consequence Operation %1 may still be executing, or ...

Adprep was unable to verify whether operation %1 has completed.
[Status/Consequence]
Operation %1 may still be executing, or it may have failed with an unknown error. All changes up to now have been saved.
[User Action]
Check the log file ADPrep.log in the %2 directory for more information. Restart Adprep.