Siemens PLC to PLC Comms Problem

I have established a link to two S7-315 PLCs via Ethernet through a CP343 card, and had active communication. The machines are now installed at the customer site, and they have an additional data collection system that polls the PLC. They did something through their network while I was at lunch and it stopped the communication between the two PLCs. I could still ping the PLCs from either machine, but the send/receive commands have stopped working. When I change the connection in NetPro to communicate directly between the PLCs and not with the CP343 card, and put a cable between the two machines it starts working again. Any ideas on why the comms through the CP343 cards would stop working due to a data collection system? I ran a diagnostics on the connection when connected through the CP343 card and it says that there is an "established" communication (see attachment). However the send/receive commands gives me an error and a status of 1.

Thoughts??????

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