ConfigurationManager return null instead of string values

Did you ensure that the config file is placed correctly at the directory from which you're running the application? Is there actually a file called <app name>.exe.config in that directory?

I'm just guessing here - maybe you added the App.Config file in a different project then your exe assembly project...?

By the way, I copied your code and App.Config as is to a clean project, and this code worked for me. So I'd look in the direction of the config file itself and not in the code. The code is fine...

Hope this helps,