When trying to open the subprojects linked to a specific project I get a 500 error

Document ID : KB000122810
Last Modified Date : 18/01/2019
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I am unable to open the subprojects linked to a project. As I try to edit the subprojects an error:
"Error 500 - Internal Server Error. The server could not retrieve the document due to server-configuration or other technical problems"

By looking to the app-ca.log file, I see the following exception that is key to this specific scenartio:

ERROR 2018-12-06 21:53:41,612 [http-nio-] niku.xql2 (clarity:admin:6499278__AC2BFB4A-4CFE-48DB-A4EF-BA8F6FD299BE:projmgr.projectProperties) Internal Processing exception 
java.lang.Exception: Invalid expression qobj: com.niku.union.persistence.PersistenceException: 
SQL error code: 1427 
Error message: [CA Clarity][Oracle JDBC Driver][Oracle]ORA-01427: single-row subquery returns more than one row 
Any Clarity PPM release
The subprojects OBS association have multiple OBS units linked to.
The following query will allow you to identify the project OBS associations:
select * from PRJ_OBS_ASSOCIATIONS where table_name = 'SRM_PROJECTS' and record_id = 'internal project ID' 

It should return one value per OBS unit.
The error is caused because it finds multiple OBS associations where it only expects one.
  1. XOG out the project and check the OBS associations.
  2. Delete the undesired/wrong OBS unit value form the XOG file
  3. XOG the project in.
  1. Delete from prj_obs_associations where table_name = 'SRM_PROJECTS' and record_id = 'internal project ID' 
  2. Now the project should open fine in the UI
  3. The OBS association is now blank. Re-associate the OBS unit through the UI