Upgrade from 8.4 to 8.5.1 fails with Duplicate MCS error after running cleanup script and manual reset of MCS

Document ID : KB000128470
Last Modified Date : 01/03/2019
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Issue:
When running the "Run Upgrade Preparation" step of upgrade from UIM 8.4 to 8.5.1 the Error "Duplicate MCS database entries have been detected" comes up.
We followed the instructions in KB000094159 and ran SQL script mysql_clean_mcs_db.sql but the error remains even though the SQL returns "It is safe to upgrade to UIM 8.51".

Then followed KB000012764 to reset MCS but same error received
Cause:
The pre-upgrade checks are failing to connect to the database and reporting this as a duplicate issue but in fact the issue is simply that the upgrade cannot access the db
 
2019-02-13 08:53:23,471 DEBUG impl.UIMServerMcsDatabaseCheckController:checkMcsDuplicatesExist:124 [SwingWorker-pool-2-thread-1] - Database error occurred: Cannot open database "NimBUSSLM" requested by the login. The login failed. 
2019-02-13 08:53:23,472 DEBUG impl.UIMServerUpgradePreparationController:analyzeDatabaseForUpgrade:413 [SwingWorker-pool-2-thread-1] - bMcsDuplicatesExist: true 
2019-02-13 08:53:23,472 INFO impl.UIMServerUpgradePreparationPanel:notifyStepComplete:151 [SwingWorker-pool-2-thread-1] - step complete: counter: 2 
2019-02-13 08:53:24,967 ERROR impl.UIMServerUpgradePreparationPanel$UpgradePreparationSwingWorkerThread:doInBackground:278 [SwingWorker-pool-2-thread-1] - Exception caught during validation checks. 
(1) error, Duplicate MCS database entries have been detected.

 
Resolution:
Ran the upgrade as the db user defined in data engine and this allowed the upgrade to complete successfully