I am trying to read StartingMonthColumn and CategoryHeadingColumn from the below app.config file using the code
ConfigurationSettings.AppSettings[\"StartingM
This:
Console.WriteLine( "StartingMonthColumn is {0}", ConfigurationManager.AppSettings["StartingMonthColumn"]);
works fine for me.
Note that ConfigurationManager is in the System.Configuration namespace (so you'll likely want a using System.Configuration; statement), and that since what you read in has a string type you'll need to parse what you read in to use it as a number.
Also, be sure you set system.configuration.dll as a reference in your project or build script.