Manastone Error: String Not Found 9190

[strugglegenerator]

So I finally got a Manastone to drop on my server and I was so excited! It works great...sometimes =p

I'll click my Manastone and it will convert hp to mana like a champ, many times, then I'll continue exping, etc and I'll go to use it again and SOMETIMES it will give me this message:

Error: String Not Found 9190

If I wait a few minutes and try again, the error will go away and Manastone will begin to function again. I'm trying to find a pattern for when it happens, but no luck yet.

Any ideas?

**SOLVED**
It only happens while in combat. So I looked up the spell "Mana Convert" in the database, and sure enough, it was set to NOT work while in combat. Why this shows as ERROR: String Not Found 9190 in game is beyond me. It shouldn't show any error, it just shouldn't work.