The error that wasn't an error

At a customer site I got asked to check an error that occured in the activity form of a Notes database. The database was a ticket database where IT service could track service requests and bug reports. Requestor said, they did not know where the error came from, but they sent a screenshot, where they had marked in red, where the error showed:



I ran a code search on the database first, lookig for the error string, in order to find out what procedure had written that error. Search result was zero. Where could that string come from? The database was a stand-alone database, no external interfaces to be expected.
Next thing, I looked deeper into the code, trying to backtrack the error source. Have you already guessed what I found? In the activity form, where the error text was displayed, I found the following computed text:

@GetDocField($ref; "Subject")

Someone had opened up a ticket with the manually entered text "Error When assigning ticket". When you created an activity on the ticket document as a reply, the subject was copied into the activity - that's why the "error" showed there, which was no error in this document after all...
The other, real error, then was fixed even faster...