Read further to know more on error:
Failed to execute RequestUserToService. ERROR MESSAGE: SmApiWrappedException:Violation of PRIMARY KEY constraint 'PK_FWSERVICE_REQUEST'. Cannot insert duplicate key in object 'dbo.FWSERVICE_REQUEST'. The duplicate key value is (501).
FWSERVICE_REQUEST is table in Identity Manager's object store database. This table has constraints defined per its primary key. You can look using a SQL Client at the table definition to learn more. The above error is a result of duplicate entry (in this case the value 501). Duplicate primary keys are not allowed in that table. This will cause any insert or update of this table to fail with the above error.
To fix the issue, use a SQL Client tool, locate the violating duplication in this table and delete the object.