Between two Windows 7 Ultimate computers. Worked fine up until about an hour ago. File sharing, web browsing works ok too.
Remote Desktop Connection
An authentication error has occurred. The requested security package does not exist
Remote Computer: Computer-Name
I found http://social.technet.microsoft.com/Forums/en-US/winserverTS/thread/7698b90a-0708-4aa2-a33b-9734de14319c and discovered that the broken computer was missing those values, but after I restored them, it was still broken.