Ethernet comm. issue with GE PLC

We currently have a GE 90-30 rack with a CPU363 processor and a CMM321. The machine also has a pc running a Cimplicity HMI to communicate with the PLC via a network switch inside the control cabinet. Everything has been in place and working fine for years. Recently we wanted to add this machine to our computer network so we can monitor the PLC program from our office building or offsite. We ran an Ethernet cable from our facility network switch to the switch in the cabinet. I also changed the IP addresses on the machine so it would communicate with our network. Now the problem, I can connect up with the PLC remotely via our network however, communication drops off and reconnects every 20 seconds or so. When I do a ping coomand to the PLC it shows 4 data packets sent out and only 2 received with a 30% loss of data. I have ruled out the Ethernet cable entirely because we put a piece of equipment at the machine and hooked up to the Ethernet cable and I can ping this quipment perfectly with no data loss and it has been working for weeks now on this cable with no issues. Any ideas what would cause this. Thanks

First thing I would do is update the firmware in the CMM321, there have been issues with earlier versions.
Next you may want to see what's going on with a port or NIC monitor like Wireshark.
Also take a look at what other devices are on that subnet and try to determine how many of these devices broadcast everything. I have seen similar symptoms when there are wireless devices that constantly broadcast lots of data to any device that will listen. We generally take care of this by installing a managed switch and limit who talks to what port. Sometimes just using a switch with "IGMP Snooping" fixes this.(Like an N-Tron 508TX)

You could be running out of connections

It takes memory for every connection. Also each connection must start on a new task or thread. This is in firmware and you don't see it but there may be a limitation on the number of connections you can have open at any time.

Another problem is closing connections. Some times connections are not closed as fast as they could be so that unused connections are not freed up.

This shouldn't affect pings though. What many don't realize is that 100 MB ethernet requires a lot of CPU power and if the CPU is running ladder and Ethernet at the same time one will have to give.

okay, I am leaning towards a hardware/firmware issue as well. I did fail to metion that we have 4 other of the same exact machines on the plant floor with the same rack, cpu, Enet card and most of the same logic program. We networked these fine and have no comm. issues. I haven't looked at the revision level of the CMM for the problem machine so maybe this is in fact an older one. I'll have to do more invesigation. Thanks