My solo kensai-mage had trouble with Imp Faldorn a while ago. Eventually i sub-contracted Cernd to take her out in a challenge, which was effortless, of course. By the looks of it, you're playing with a custom party and are unable to temporarily drop any members, yes?
Edit: After checking the old post, it seems that Cernd has to be outside the party to be able to do the bypass. Check Imrahil's advice in
this thread and you should have no trouble.
