All right, I found the problem and solution.

I had added some custom methods to the main application class -- general utility things.

Some of them were data handling routines and had to be passed the datasession.

Naturally I also intended to save the data session of the utilities and set them back.

The problem of course was that I made a logic error and failed to this. This caused no problems when testing a form by running it once and exiting the application -- since returning from the method back to the calling form found the data session set properly. But it left the main classing running in the private session rather than the default one -- which was only detected when I tried to run a form a second time.

Bottom line -- if you add methods to your main class which mess with the data session may sure they set it back before returning.

Thanks