As mentioned in the incident report notes, you must make sure to take additional steps if you have altered any Unicode database objects using DDL statements since 2.15 was released:
This error affects the database catalog, so if you have altered any Unicode databases using DDL statements such as ALTER PROCEDURE, ALTER TABLE, etc. then you should re-execute these same DDL statements using 2.15 Build 3 and that will correct the issue.
The problem was caused by the internal ID used for the Unicode collation being set to 1 instead of 0. This would cause the ElevateDB Manager and other internal code that uses the Collations table for looking up collations to use the wrong collation ID. This problem did not affect ANSI databases, only Unicode databases.