Hi,
MachScreen saves the loaded file with the filename and an incremented number in the file-extension. If you haven't loaded your set-file more then five times, you could try the following:
Rename your file THC300M3.set to THC300M3.old
rename TCH300M3.SEn with the highest number to THC300M3.set
try to load the set-file. If this doesn't work, I'm afraid you have to ask your dealer for that file again, or you use another set-file like 1024.set, if that fit's your demands.
Klaus