I created a new 4.2 project. Moved all the code over from the 4.1 project. All the libraries are either 4.2.0.0 or 4.2.0.1, or something I built under 4.2 and added. Everything builds fine. When debugging the Sample Emulator appears for about five minutes and then quits with the output: "Error: Error in the Application." Before creating a new project from scratch, I got "Error: Assembly file " does not exist! Load failed." Suggestions appreciated. Not much to go on, I know. As always I'll keep trying things.
Chris