While attempting to log onto an Windows Server 2008 R2 system with Exchange 2010 for the first time, I received the following error: "User Profile Service service failed the logon. User profile cannot be loaded."
After much searching, we found that during a reinstall some bits were left in C:\Users\Default\AppData\Local\Microsoft\Exchange Server
Once the files therein were removed, I was able to login successfully. We surmised that since the files were in the Default profile, something was stopping a new profile from being generated.