I've just identified the cause of this, -32000 is returned as the screen location when it is closed while minimised, ive just added a few lines that restore the program if it is minimised on exit.
During startup the config file is loaded, or created after which I added code to check that the form location is within the bounds of the display, and if not it is reset to 0,0. It seems that there is a logic error with this, I'll fix it for the next build.