Yesterday I ran into an interesting issue where trying to reassign an expense report from one manager to another resulted in the error:
ORA-20001: Exactly one of an approverRecord's person_id and user_id fields must be null. ORA-06512: at "APPS.WF_ENGINE", line 5931 ORA-06512: at line 1
This error message obviously doesn't make a whole lot of sense, so off to My Oracle Support I went! I found note 1299908.1 that seemed to be fairly on point, but when I looked neither employee had vacation rules set up and bug 13616552 didn't get resolved yet so that wasn't any help. Pinging one of my co-workers about this, he knew what was going on with this and asked if I was choosing to transfer the notification or delegate the response. I wasn't prepared to find out that this happens at times when we choose to delegate the response for notifications to another manager, but on the same record if you choose to transfer the notification to another manager no error message pops up at all! This seems like such a small thing, but I typically use delegate to switch manager assignments in the system and apparently at some time we introduced this bug into our system.