I'm assuming that happens when you're logging in? If so, please read through our
Facebook Application Setup Guide
. That error usually means there's something wrong with your "Valid OAuth redirect URIs" in step 21.
Take a look at that step and make sure everything is as shown in the guide. If it already is, let us know when you get that message (if it's not during logging in) and we'll gladly help further.
Thanks,
Alex