Never seen this before, not sure if it was something to do with my client, but today when I logged in I got this message a few times at seemingly random intervals
Saw the same thing my end!
Script errors are broadcast to everyone who is currently logged in even if they had nothing to do with the error. If it seems to happen in response to any particular action you are doing at the time, then you should include whatever it was you were doing at the time in the bug report.
It doesn't sound like anything you did caused it if the intervals seemed random though. Since someone was doing something that had to do with the spell, It would help if they mentioned more details with what happened when the error popped up, if the spell failed/worked etc.
But I'm willing to bet Mort broke it.
Fixed.