I never did get that lock open but then, I never finished my second playthrough, I got Baldur's Gate recently and I've been playing that. You should be able to open it though if your Locks&Traps skill is level 7 or highter with a Lv 5 Lockpick. Lockpicks can open jammed locks. Or else just try casting Disarm Trap. That should get it open. I've never seen Disarm Trap fail and it can also open jammed locks.
-Jafin
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I am Jafin, arch-mage of the HADB clan!