Dug around a bit to get the gista nd found this on Rockwell:
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A939693 - How to configure RSView SE to use RSView32 OPC Server as a remote data server
This suggests that there is one defined that may no longer exist as defined. Have you done any server name changes or changed an ip address structure lately? I recently changed the ip address scheme on our whole process system so that it would live comfortably on the same leg as the business network without interaction. Was not pretty, but once done allows me to Term Service in as needed and manage remotely. It aslo saved some expense on a Domain Controller as our business PDC acts as that for the HMI servers (RsView SE pretty much requires it for failover redundancy to work) --and this works only because those servers have 2 NICs that allow them the straddle both networks.