"I saw your thread and wanted to reply, but can't post in Premium. Anyway, this is just an off-hand guess, but try removing the "%3Bcid%3D" and the data following it from the end of your URL, and seeing if that works.
That "cid" parameter seems to have something to do with login cookies, meaning that it should be specific to your computer. That could be what's interfering with the registration process."
This makes sense to me because that link always has my email address in the field. I'll try it, or would appreciate a confirm from H/P.