what are you using for motion control?
does the machine run smooth or does it have resonance?

I had this problem with my old xylotex drive  The solution was a dampener.

I tried disabling the a-axis, but the results were the same.

Rich, this is the latest released version on the website (vR3.043.022 -- lockdown) is what is installed; is that not supported?

I think the problem is that version R3.043.022 is not compatible with the Pirate license file you are using (please correct me if I am wrong).

Tweakie.

Tweakie
 It is a genuine licence, not sure if its the original owner but looks likely
Hood

lcluff2000
Cant see why you would be having issues unless your computer is just on the edge, have you run the driver test at 35KHz to see what it looks like?
Hood

Tweakie
 It is a genuine licence, not sure if its the original owner but looks likely
Hood

If that is the case then my sincere apologies.

(Software4u was used as the license name on one of the pirate copies I looked at over a year ago).

Tweakie.

I had my doubts about it as well but Scott confirmed it was a genuine licence and was from a long time ago. Cant be sure its the original licensee but it is a genuine licence name.
Hood

Not sure what the problem is.  
Are you using the default Mach screen?
Are all the steppers the same? Have info on them ? Post model number, in-oz, size.....
What drives are you using?
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Since the x & y are working properly,try swapping the cables to the motors by using the x or y cable for the Z. What happens?
If the Z stalls then lower the velocity to 15 for the x or y and try again. What happens?
Now use only  the x or y cable to the Z but at 45IPM. What Happens?

RICH

Thanks Hood.

My apologies to all concerned.

Tweakie.

No problem Tweakie. Yes, I did own a company named Software4u and paid for mach probably ~6-7yrs ago.
The motors are 23H276-28-4B XYLOTEX 269 oz-in on 3 axis. The 4th axis is a Moon 17HD4063-01N (but I disabled that axis yesterday and the problem still exists).
The drive is XS-3525/8S-4. The vref is set to ~3.2v (on 3 axis) which translates to ~2.2A, the 4th axis is set to 1.2V (0.83A). I'm using a 24V power supply.
The problem occurs on all 3 axis'. All 3 axis work at 45IPM (independently) when I jog, but when I zero (independent axis') or use program control the motors stall.
I'm using the default mach screen

I'm running out the door right now, but I'll try the following experiments tonight:
(1) driver test at 35khz
(2) swapping cables to motors