At some point after you have been to Stormfist castle (don't recall exactly), Mardaneus gets locked in his house and the ladder gets removed from the cellar. Once you rescue Zandalor and let him teleport you somewhere else, clear that area and start another quest involving Mardaneus (that Zandalor will tell you about), you will be able to head to Aleroth and (after dealing with the situation there) be able to complete George's quest.
BTW, you should talk to Mardaneus about George first, as a couple people had trouble doing that after talking about the new stuff.
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