[TwoHandedSword]

There's a glitch from one of the hexed weapons in the Tarant sewers, that makes its curse permanent once it's been equipped. The Blackstone Blade, IIRC.

If you unknowingly equipped it, the only fix is to return to a saved game from beforehand -- or, regrettably, to start all over again. There might be a patch available by now, but I don't believe patches can be applied after the fact.

Sorry to be the bearer of bad news. But at least now you know.

(FTR, there's a similar glitch with the Dark Helm that also makes its effects permanent: +4 to your MA, in return for a -20 alignment penalty, every time you equip it. While technically also a bug, this one is at least useful: you can maximize the benefits of arcane weapons and armor, with but a small hit to your max alignment, and without using up all your build points buying spells.)