Direct Technology .NET Developer Mid-level interview questions

They started with FizzBuzz which is easy for someone with a little bit of experience programming. Passed. Then 2 developers come in. They talk briefly, didn't even really introduce themselves and load up an app which I am to debug using VS 2010. I breezed through the initial bugs noticing and correcting them quickly. Then I came across stuff I'd never needed or done in programming before. As a consequence I'm mildly baffled but I'm trying to figure out what they were doing when I get told to move on. The rest I completed. They ask me questions, I ask them questions and we're done.