Error when trying to extend range using an Extreme connecting to a Express

Ok,
My cable modem is connected just fine to my AE. I can run iTunes (which is nice!) off of it, connect to the internet off of my MBP and all. I just bought a AEBS to be able to EXTEND the range of my connection for all of my small townhome. However, when I go to through the Airport Setup Assistant to try and set it up, it keeps coming back with an error that says "Error Setting up WDS" or something like that. I've tried this multiple times. I've tried resetting both the AE and the AEBS...still doesn't work. Any clue?

Thanks,
Ryan