Louie,
I'm not familiar with the C1, but I have a C11, and I know the early ones used fast optos only for the step signals, and slow optos for all the others. On mine, the slow ones were REALLY slow. The current C11 uses fast optos for all signals, and works much better. I'd suggest you look at your board, and determine the revision level, the contact Arturo at CNC4PC, describe your problem, and suggest this might be the problem. At a minimum, he can tell you which are the faster outputs. Are you using the outputs he recommends?
One thing you can try, to determine if this is the problem, is to connect one axis connecting the DIR signal through the output you normally use for the STEP of another axis, and see if that one axis now works correctly. If it does, then I think you have a smoking gun.
Regards,
Ray L.