What is your network?
Is this ethernet, the coax networking, or?
With ethernet I once had a problem like this and had to do a factory reset on the router, as it seems it had a glitch that was blocking a port.
Didn't realize he was using Ethernet for MRV. The only problems I had with my Ethernet MRV was using too many HRs. With only 2 HRs, I'd think it would work perfectly. I'd switch locations of the two HRs and see what happens.