We're getting a 'Procedure cancelled' error (undocumented) and we can't figure out the actual cause of the error.

I had a theory about timers trying to execute a SQL server query while another longer running SQL query was running, but I just tested the heck out of it and could not repro it.

Does anyone have any experience with this error? I've googled and have come up with not many items and they didn't answer my question, IMO.