We have AAM set up almost exactly like the link above, with one exception - In Central Admin - Operations - AAM, we don't have any addresses set up under the "Internet" zone. We only have mappings set for the following zones - default (internal url = public url for zone), and Intranet (internal url/Public url = extranet.servername.com & internal url/Public url = extranet.isa.extranet.com). Would this be the cause of the issue with the form not opening correctly?