MAC receive errors, sublayer recv error

Hello All,
This is my first post and I need a little help. We are experiencing a problem with our network communications.
Using RS Logix 5000 Ver 15, Control Logix PL-63 Processor. Every so often we are loosing our Ethernet communications to our processor. This effects comms with our wonderware MMI's and trends and breaks the online connection with our programmer. The ethernet card is type 1756-ENBT/A Rev 2.3. We have checked cabling, network usage, swapped ports on switch which is Cisco. We have reseated the ENBT. It lasts for 4 minutes each time, and then everything begins talking again. Does this seem like a PLC issue or a "something is interrupting" the flow of data isssue, or what? Also under proporties of ENBT card, under port diagnostics we show a rather large number next to MAC Receive error. This value does not reset when we reset counters. What is MAC Receive Errors? and how do we fix. Any ideas?

MAC recieve error is a corrupted data coming from the wire

most likely you have ENBT dulex forced while switch port remains in Autonegotaiation or vice versa

Set both switch port and ENBT the same

I recomend Autonegotiation - thisis default outof box state and will help with module replacement in future.

If this is unmanaged switch, then ENBT MUST remain in autonegotiation.

Unrelated:
FW 2.3 is very old, it will be better to upgrade it to something current.
3.9 or 6.2 two versions I would go with