This used to be caused by the installation of .NET Framework via Windows Update.
This also used to be solved automatically with the installation of the .Net Framework Service Pack.
On the systems that I've built recently, I noticed that this is no longer corrected by the Service Pack installation and has to be manually corrected on some systems.
Click on Start>>>>Run.
Type in control userpasswords2.
The account manager will launch, from this you can select the account that you want to log on to automatically and enter any desired passwords that might be pertinent.
Reboot and test when finished.