I often write new code and I get errors such as "'System.Array' does not contain a definition for 'ToList' and no extension method 'ToList' accepting a first argument of type 'System.Array' could be found (are you missing a using directive or an assembly reference?) ".
In the above case, I was missing the "using System.Linq" directive. I usually google the error and I find out what directive I need to add to the project. Is there a better way of finding the missing "using" directives from within SharpDevelop?