>You should type ConfigurationManager.
>
>I do not think that you understand my problem. This does not work. Even if I type System.Configuration. ConfigurationManager is not there in intelliSense. The only options I have that begin with the word "Configuration" are ConfigurationException and ConfigurationSettings.

Did you try it multiple times after re-starting VS? I had sometimes Intellisense lost for unknown reason. Re-starting VS usually cures it.