Hello ,
Hope you are doing well.
Please try to load a regular example it looks like you may have lost connection to the target. Set the switches to serial downloader 0,0,0,1 then flash a blinky for example. Once it is working again you may set the switches back to 0,0,1,0 and try debugging your flash loader demo again. I had no problem loading the demo imported straight from the SDK without any additional modifications.
Best Regards,
Sabina