Centroid Community CNC Support Forum

the grounding in the box doesn't look that great. you might have a ground loop going on.
wouldn't hurt to swap out the CNC PC (change one thing at a time) as a test as well.
use the com stress test as the final determination, ive seen system pass a ping test but not the stress test.

If ping works and CNC12 can't connect, then I suspect you have a firewall problem. Verify that CNCM.exe is added as an exception in Defender.

It's not enough to turn Defender off. Windows turns Defender back on whenever it feels like it.

Another thing to check is the Ethernet adapter's link speed. Search here for threads mentioning this. IIRC some have to turn this off automatic and force a specific speed for some brands of Ethernet adapters.

Also check the Windows Anti-Virus. I have to turn mine off every time I start the machine, even though I have it disabled in the Policy editor.

Try setting your PC Ethernet port speed to 100Mbps - Half Duplex as Tom mentioned. This and making sure the AV is off worked for me.