How can I access ConfigurationManager.AppSettings in my Windows Forms Application?
The error message reads: The name 'ConfigurationManager' does not exist in the current context.
Add a reference to System.Configuration.dll.
I've had this experience before where I had to go and add a reference to System.Configuration to be able to use this funcitonality.
Right click on your project in the solution explorer, select Add Reference then select the .Net tab (it should be selected by default), and select System.Configuration
来源：https://stackoverflow.com/questions/1796851/unable-to-access-configurationmanager-appsettings-in-a-windows-forms-application