More accurately, it revisited me again.
Every time I search for another answer, I usually get the setting for
the startup - and I always check and mine has always been ok. Very
This time, it was an error in my resource dictionary (XAML) on one of my styles. There were elements the style was bound to that had been removed.
This gave me the "Catastrophic Error" and when trying to run I got the dreaded 2103 code.
I remembered the last style I had added, and looked over that since Silverlight ran right before the changes were saved. The elements of the style had that squiggly line (in VisualStudio 2010 - it's one of my "technical" terms) that let me know where the error was.