We used to get this error quite a bit. Especially, after we changed the Windchill configuration, 'Send a CAD document Dynamic Document to PDM without optional Dependents' to True.
While that setting was set to True we would get these errors once every 4-6 weeks. After a lot of troubleshooting we tracked the cause down to the above mentioned setting. After we set it back we have not seen this error since.
However, when you get the not persistent error, it almost always took a database level manipulation to fix. PTC tech support finally issued us a patch after quite a bit of work to clear up our last remaining errors.
So the recommendation is to leave, 'Send a CAD document Dynamic Document to PDM without optional Dependents' at the default False setting.
-marc