The "One of the spells has failed" message

When a creature I made is hit, it sometimes displays this message. What does it mean - that one of the hit one's spells has failed (this one is supposed to cast a spell on being hit, but it's wired into an item and should not fail for any reason)? Or does it mean a spell cast on the creature has failed (this one also has lots of spell protections)?

Target is out of range of the spell trying to be cast.

That must have been it. The spell did have a very short range. Thank you!