You got the lamphorn before Jaheira leaves? Then you haven't finished out the plot thread with Jaheira to lay to rest the conflict with the Harpers. I am (95% positive--it's been a while since I did this) that you have to have three encounters. Someone correct me if I'm wrong. Have you tried clearing up the mess with the Harpers's (Jaheira leaving, etc). before getting the lamphorn. Do you have a save that goes back that far?
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O_H_F
