When did you download the upgrade package? There were some problems related to UI elements which caused this error and it should have been already fixed. If you have not downloaded the package in the last few days, please do so and roll back the backups and perform the upgrade again.
It seems that there is an inconsistency in the DB. Could you please check the CMS_UIElement table and search for any records that have the same ElementResourceID - duplicates? If possible, I would recommend to remove the duplicates form the DB and then try to repeat the operation.
Please let me know if you have any additional questions or concerns.