AFAIK, this is lower-level error coming from Microsoft RPC or DCOM that normally "should not" happen. Looks like that the two ends do not really match well. Can you please check:

- That the operating system have service packs and updates. BTW, is the client and the server running on the same OS?
- That both systems (client and server) have the same version of OPC stubs/proxies (i.e., the same version of OPC Core Components).
- That there are no network configuration problems (see e.g. the discussion here: stackoverflow.com/questions/10027454/create-com-object-on-server-in-c-error-80070776 ).

Note: If the only OPC software on the server side is FactoryTalk, the OPC proxies/stubs may be included with its installation, and you won't see any "OPC Core Components" in "Add/Remove Programs". In such case, I still recommend installing the recent OPC Core Components from OCP Foundation, which will update the proxy/stub already residing on the system. opcfoundation.org/developer-tools/developer-kits-classic/core-components/

Normally I would advise you to try to assign different combinations to following static properties - in the code, before the very first OPC operation is attempted:

EasyDAClient.ClientParameters.UseCustomSecurity
EasyDAClient.ClientParameters.TurnOffActivationSecurity
EasyDAClient.ClientParameters.TurnOffCallSecurity


(if you are working with the demo app, then there is a source code to it available under examples).

However that is usually needed when there is a permission problem such as "Access denied". But it may still be worth trying. Your error ("RPC Server is unavailable"), though, seems more related to issues with processes running (or not running) and/or firewall access. Are you saying that even the firewall that's on the client side is turned off?

Do you have some other OPC client to try from the same machine, and if so, what are the results?

This is perhaps the most common question. I suggest that you start by folowing the steps described here: www.opclabs.com/resources/technology-opc/opc-videos/opc-dcom .

Best regards