Running out of ideas. You could try this - it worked for me once or twice.
Working in a Linux terminal, first I did
Then did
This presented me with the following:
WARNING: DOS-compatible mode is deprecated. It's strongly recommended to switch off the mode (command 'c') and change display units to sectors (command 'u').
So I pressed the following
c and
u followed by
d,
1,
d,
2,
d,
3,
d,
n,
p,
enter enter and finally
w. I think that they are the correct letters and numbers - you'll suss it out if not.
This scrubbed the device. I then gave Roobarb's reflash tool another go. Once again, it went through the motions but, lo and behold, one the first attempt the Joggler fired up and booted straight into a nice clean stock OS!
Otherwise, it probably has gone wrong for ever!