After upgrading from Liferay Portal 5.2, permissions settings may act in an undesirable manner. This could include not being able to change permissions, as well as not being able to access the control panel or any other areas of the portal that require something other than guest permissions.
Resolution
The permissions issues are caused by not having properly set the permissions algorithm. If upgrading between Liferay versions that use two different permission algorithms (permission algorithm 5 - Liferay Portal 5.x and 6 - Liferay Portal 6.x), this runs the risk of corrupting permissions for users. An upgrade will not convert algorithms, and must be done before or after upgrade.
To resolve a corrupted permission set due to not setting the algorithm properly, the database must be rolled back to the un-upgraded state, and then re-upgraded with the correct permissions setting for the database. Permission algorithm migration can be performed before or after the upgrade.
For Liferay Portal 6.2:
Please note that Liferay Portal 6.2 uses only permission algorithm 6. As such, if on another permission algorithm, permission migration is required before the upgrade.