A final solution:

I have got the thing back on track now. But, I'm not sure what I did to fix it. Of course, I tried several things and now it's fixed. I think the last thing I did was to move the offending form up to the root level of the project . . . and then back again. Maybe re-copying it organized some dependencies. I also changed the name of the start-up project so it was not the same as the solution! (don't see why that would make any difference). Another thing I did was change the order in which the dependencies are compiled.