What kind of machine are you currently using? And what motors and drives?
With homebuilt (and even cheap ready to run) machines, sometimes frequent adjustments and alignments are required to keep them operating properly.
The slightest amount of misaligment can cause binding of the motion components, leading to stalling and lost position. Even changes in temperature can cause issues.
If the jog keys were working before, it's possible that the .xml file became corrupt.
The .xml you posted doesn't seem correct? It has a parallel port address, and no motors set up in motor tuning? Maybe because I don't have an SS, but it doesn't seem right.
As for the Greenbull....
Just my opinion, but I think the Build Your CNC stuff is all overpriced and underperforming on many levels. They seem to have a large community of happy users, but to me they don't have any idea that there are far better products out there. Take a look at CNC Router Parts, for a much more rigid, all metal machine, that will run circles around the Greenbull for about the same money.