6i25 and 7i77 config

Does the pc have a metal housing (shielded), with the 6i25 inside? Or is it a motherboard mounted in a cabinet that also contains a VFD, relays, etc? If so, your motherboard will likely need additional shielding.

Yes the PC is in metal housing and right now it is outside the control cabinet. I am confident this is not a EMC issue.

i have bought a much older pc which i will test tommorow.

thanks so far.

Just to end this topic: i bought a new PC and LCNC booted up. So the issue was proberly that i used a too new PC with buggy/Incompabtible PCI-E.