Need Help - Arduino Mega, RAMPS 1.4, TB6560, and Repetier!

I built a CNC milling machine I want to use as a 3d printer and cnc mill. I am using Arduino Mega and ramps 1.4 with lcd and sd card reader. I am running repetier firmware and repetier host. I am using TB6560 stepper drivers instead of the A4988. The problem I am running into is that when I connect to the board with repetier host I get an error message "the board is not functioning", when I disconnect the TB6560 drivers from the board, repetier host connects to the board without problems.
I connected the TB6560 drivers with the RAMPS board as follows:

STEP to CLK+
DIR to CW+
EN to EN+
CLK-, CW- and EN- to GND

What could be the problem in this case?

Should work...

A friends of myne did just this some time back

[andre.team9.99.org.nz]

Maybe there is something there you can spot

Edited 1 time(s). Last edit at 03/31/2015 07:15AM by Dust.

Thanks "Dust" for the reply.
I already checked this link some time back, I followed it's instructions and still having the same problem.
I also flashed Marlin firmware and tried to connect with Pronterface while TB6560 drivers are connected and active, Pronterface couldn't connect. When I disconnect the drivers I'm able to connect to the board. So I believe it's not a firmware nor software problem, it is related to the drivers and serial communication.
I'm assuming that somehow the drivers are interrupting the serial communication.
Any idea what's happening in the serial port?

One more thing, the TB6560 are driving the stepper motors nicely when I 3D print from the attached SD card.
This confirms that there is no defect or short circuit in the board or the drivers.

Im thinking some sort of ground loop as serial comms is no where near stepper side...

If you have you steppers drvers powered off but connected can you still talk to the mega?
What about with stepper power unplugged?

I can talk to the Mega when steppers power is off, and I can talk to the Mega when stepper power unplugged.