On your circle file is it a .dxf file that you import into kcam? First try this file. It is 2 circles a small one and a big one. Under kcam menu import the dxf file.
Also just a guess as I had a similar problems with a different driver board and I set the DIP switches to I beleive micro-stepping and had no problems after that.
You might also check in kcam to make sure you ran sysem timing as that helps the motors run more efficiently on your system.
On your X,Y,Z speeds under table settings set feed rates to 8 for x,y,and z,... and also set the maximum speed rates to 10 for each axis and set the ramp rate to 5 and maximum ramp rate to 10 ....make sure read about the backlash settings. I forgot what I had mine set to. I know its slowing down your system but this will help you see what you are doing as well as testing the hardware. If it works at slower speeds then you know you have a hardware/electronic problem.
If all the above doesn't help Try contacting Kelly at KCAM. It might take a a day or so for him to get back to you but the support from KCAM is outstanding. Make sure and join the KCAM forums so you can post questions there too. There are Gurus both on CNCZONE as well as KCAM forums.
Hope this helps.