800706ba RPC Unavailable with OPC




We are trying to establish OPC communication between a Windows 2000 Server
SP4 server running OPC Client and a Windows XP SP2 workstation running OPC
Server. When we try to establish communication interactively, we get

"Advise returns error: 800706ba(The RPC server is unavailable."

and cant figure out why. We have successfully installed the same
configuration in two other places with identical computers and they work fine.

Here are the specifics:
Windows XP SP2: Firewall is turned off. OPCEnum service is installed and set
to automatic. DCOM defaults are Connect/Identify with DCOM enabled. OPC
Server is set to run under an account (opcuser) with administrative rights.
Both OPCEnum and OPCServer DCOM Access and Launch permissions include:
Interactive, Network, System, administrators group, opcuser, everyone

Windows 2000 Server SP4: No firewall or antivirus installed. OPCEnum service
installed and set to automatic. DCOM Defaults are Connect/Identify with DCOM
enabled. OPCEnum DCOM permissions include Interactive, network, System,
administrators group, opcuser and everyone for both access and launch
permissions. The OPCEnum service is also set to run under opcuser account
with admin rights. Registry records for the OPC Server running on the XP
machine are created on W2K machine with the OPC Server's client setup program.

When we run an OPC client from the W2K Server computer, we get the list of
servers available at XP computer, when attempt to connect, we successfully
connect, create OPC Groups, browse tags and add tags to the group. When asked
to advise the group we get the 800706ba message.

Things we have already done:
1) Checked the versions of MDAC (2.6 SP2 and 2.7) with a tool available from
Microsoft. No version conflicts. Reinstalled 2.6 SP2 to be sure.
2) Checked for msblaster virus using Symantecs Fixblast.exe tool. None
found. Microsoft's patch for blaster virus wasn't installed. Installed the
patch. If I remember correctly, blaster virus would ask to reboot the machine
frequently. No evidence was found in the system and application log files for
periodic reboots.
3) Reinstalled SP4, restarted. Didn't work.
4) Searched for "svchost -k" entries in the registry and replaced them with
"svchost.exe -k" . Didn't work.
5) Checked under HKLM and HKCU registry hives for unwanted entries. Removed
6) Checked Autoexec and config files. No questionable entry was found.

We ran out of ideas. Any answer or help or direction would be highly


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