This one drove me nuts for four days before I figured out what was going on. A client is deploying OCS 2007 R2 in their environment and ditching WebEx and GoToMeeting, as well as the other conferencing and collaboration features of the product.
However, the main goal of getting users outside of the organization to access meetings was just making me rip my hair out. No matter what I did, each time I tried to join a meeting it would pop up and demand credentials on the client’s domain. All three of my external test machines did the same thing and I could not, for the life of me, figure out why.
A quick search did reveal some permissions issues, and I corrected them according to KB 2018725, and they are running Windows Server 2008 Standard x64. After setting the permissions, though, I still had issues.
Finally, I managed to find a Microsoft forum post that explained it all. When I was testing the external access with the MOC client, I was logging in to the client’s network as my domain user. That was pre-populating the user information in LiveMeeting with my SIP URI information on the client’s domain. Deleting the account info instantly fixed the issue on all three test boxes. In addition, three new user machines that had never before connected to OCS were able to connect to a LiveMeeting session without any errors or prompts.