Hello,
The help file is a CHM file. You can open it from the start menu:
Start > All Programs > Renegade Minds > GDT4 > GDT Help
In the program folder, the file name is "guitar_and_drum_trainer_v4.chm".
The bug there is fixed in the current development version of GDT and will be in the next release.
Cheers,
Ryan