Huanyang VFD control plugin for Mach3, USB RS-485

[JayPunchbuggy]

If it is interference then what can I do to fix the problem??

You could try:
1) make sure the shield of the RS485 cable is actually earthed by the checking the continuity of it to the PCs chassis
2) Ensure that the RS485 cable is not run near sources of interference, like the spindle cable. Especially avoid running the RS485 cable parallel to any other of these cables.
3) try a lower baud rate
4) reposition the USB to RS485 converter

Hope this helps! To suggest more, a photo or more detailed description of your wiring would be useful.

Cheers,
Jay