ConfigurationManager.AppSettings Error

hii all!

When i tried to access a value from the configuration file (ConfigurationManager.AppSettings("ADMIN"))
i am getting an error:
'ConfigurationManager.AppSettings' is not declared or the module containing it is not loaded in the debugging session.

can you please anyone help me who have experienced the above said error

thanks in advance,

best regards,

Ammar.

(platform: .NET Framework 2.0, VS 2005, SQL Server 2005)