Suddenly modbus error

[ClausP]

Hello everyone  

Since august I have had a huge problem with my modbus RS485 on my W4K.
I have a Carlo Gavazzi EM340 energy meter and a Nilan CTS602 ventilation system connected to the W4K through modbus. 
But since august last year, I keep getting Operation timeout on the EM340. It still sends its values, and til W4K puts them in the trends.
The big problem is, that the control for my  ventilation has stopped working with a Invalid CRC error. 
I have tried everything. 
New EM340.
New mainboard in the vent.
New W4K.
New Cables between everything.
New ethernet cabel.
Ethernet directly in the computer.
Downgraded to firmware 2.8.2 from 2.8.3 thinking that it maybe was a firmware error. 

But still no luck!! 

I have spoken with Schneider technical support for hours. And still no luck?

Does anyone have an idea to what could be wrong? 
I still do suspect that it could be a firmware/software error?

[Daniel]

Do you have GND connected?

[ClausP]

Do you have GND connected?

Yes. GND is connected between W4K and the devices. 
I have not connected the GND directly to the protective earth of the installation.

[admin]

Have you tried leaving only one Modbus device connected and checking if there's any change in the behavior? Also check that AC L/N is connected correctly to all Modbus devices and your W4K DC power supply.

[ClausP]

Have you tried leaving only one Modbus device connected and checking if there's any change in the behavior? Also check that AC L/N is connected correctly to all Modbus devices and your W4K DC power supply.

Yeah, right now I only run one single EM340 on the bus, with 50cm cable. I have switched the powersupply for a new one. And I have changed the N/L arround to try both configurations. 

Once again, It has run flawlessly for about 3 years.