I am gonna guess you are running the SoF client. I believe that problem happens when you have a spell file that does not match the spell file the server you are on is running. If you downloaded a custom spell file for playing on one of the servers you play on, that is likely to be the culprit. When you download custom files like that, it is always a good idea to backup or rename your original files instead of overwriting them. That way, if something goes wrong, you can always revert back to the originals.
You might be able to find a file download on one of the servers you play on the most that will work to replace the bad one you have. You can always give the one from my server a try and see if it helps at all:
http://stormhavenserver.com/mediawik...l_Custom_Files
In particular, you want the spells_us.txt file. You could also just remove EQ and reinstall it fresh to restore the original spell file.