Did you talk to Zandalor and go through what he has to say first? I don't know if that is required to trigger the speech options with the imp, but the imp should have a lot to say.
If talking to Zandalor doesn't help, you can get another copy of the teleporter stones;
Lost Items - guide and directory of inventory files

or wait until you get to the wastelands to find replacements;
location of the Ancient Pyramids (71KB) - if you did not bring both teleporter stones with you to the wastelands