I upgraded a Windows 2008 R2 Standard server to a Windows 2008 R2 Enterprise server while it was still part of an existing domain. I then removed the server form the domain and made part of its own Workgroup. Now, when I try to re-add the server to the existing domain the GUI, where you make a stand alone server become the Member of an existing domain says the following:" You can change the name and workgroup membership of this computer. You cannot join a computer running WIndows Server 2008 R2 Enterprise to a domain." The area where I can type the existing domain that I want this server to be part of is now dimmed out. Please advise.