G320 Position Error Fault

Hi all,
I have been tunning my G320 servo drive for a big Fanuc motor every
thing went perfect , I can jog smoothly accelerating and decelerating
to full speed with out any Position Error Fault LED lights .
The Problem arise when sudden stop happen ( when stopping a G00
command by pressing ESC on the keyboard ) the Fault LED lights

The 128-+ counts are too little to stop a big Inertia motor !

The Damping Trimpot is at full scale , Gain and limit Trimpots 3/4 of
full .
I reduced the full speed (from Mach3)it helped solving the problem but
not a very practical solution !
What should I do ? Is there any way to increase the 128-+ counts
error or eliminate it ?

Thanks,
Shadi Salhab