MMm all traps can be detected I think, I did not have any problems to do it. Cast detect trap by you'r cleric ( if you have one ) and try again disarm it. If you can't again, just improve your stats .. I think there is traps that need more than 100% in stats to disarm it ...
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Maybe it's because I hate drows more than I hate Humans - Jarlaxle to Entreri