Building Windows Phone app (app keeps closing on startup when building in VS Express 2012 for Windows Phone, but no bugs/errors found)

After integrating Admob into my Unity3d-made Windows Phone 8 App, the app keeps closing on startup when I try to build it in Microsoft Visual Studio Express 2012 for Windows Phone. Both on a real device and in the emulator (I have the latest updates), after it opens, it immediately quits. Note: Before I integrated Admob there were no issues. Please only respond if you know what to do. We will work via TeamViewer.