NullReferenceException when closing main form

[hypa_dude]

I have written a Windows Form Application (standard c# template) in Visual Studio 2008. When I try to close the main form of the debug build, I get an unhandled exception that I can not figure out how to resolve.

//program.cs

...
static void Main()
{
Application.EnableVisualStyles();
Application.SetCompatibleTextRenderingDefault(false);
Application.Run(new Form1()); //NullReferenceException
//"Object reference not set to an instance of an object"
}
...

Before today, my application was working fine. I'm not sure what I changed to make this happen. Are there any suggestions on where to look and/or how to fix this?

[Hack]

What changed in your envirnoment since yesterday when it was working?