Has this issue been resolved? I have run into it as well, just having installed and trying to use AD on 4.8.2 for the first time. I have a very similar config as Maxime.

Okay I can recreate it.

Something must've changed in the core when 4.8.2 was released or maybe back in 4.8.1 that's causing the issue and I missed it because my user account was already part of the database.

I'll see if I can get it fixed this afternoon and put out a beta for you to try.

Robert,

In your web.config make sure the second <add name="Authentication"..../> (should be at the bottom of the group) in the <httpModules> section is uncommented. If it is then clear your cookies/cache. As long as the cookie is active it'll skip the authentication process.

Everyone else in this thread:

I've found the problem. The user account is created and a "Success" status is returned. However in one of the latest versions of the core the Success status is no longer checked so it returns the error message. It's an easy work-around in the code but I need to check if there's going to be any problems in previous versions of DNN. I've logged the bug in Gemini http://support.dotnetnuke.com/Default.aspx?p=28&i=7243 so you can keep track of when I check the code in.

I may also take a quick look at some other bugs that I have an idea how to fix before I release a beta but will try to get something out before the end of the weekend.