Remote server cannont connect to this machine

Question

I'm using datasockets in Labview 8.5 (Evaluation copy) to develop an OPC client application
to connect with a remote OPC server running Kepware.  I've tried a number of different
ways with no luck.  When I try to connect using front panel connections, I get the remote server
error cannot connect to this machine (check local permissions), but in the event log, the logon
audit is a success.  So I'm not sure what permissions need to be changed.  So far I have changed
DCOM security settings to allow Network user, the name of the OPC server, anonymous, everyone, access
permission for both local and remote and the same in launch and activation permissions.
I've tried using the NI OPC Client example and I just get an error 42, generic error.  I have spent my wheels
with this one and no prevail.  I downloaded the OPC Quick Client from Kepware, which I can use to connect
to the OPC server, but I do get a Failed to connect to 2.0 data access for group ...., but it still displays the
values once the items are selected.  NI Server Explorer works just fine and Iconics also.  Has anyone run
into this problem before and how did you fix.
Thanks,
Jay

Answer 1

Typically if the Kepware OPc Quick Client cannot connect to the Kepware OPC Server there are possibly more than DCOM issues involved. The first thing that comes to mind is that the OPCproxy.dll and OPCcomn_PS.dll on the 2 PC's are out of Sequence. You can easily verify the versions on each PC.This files should be located in the system32 folder.
The next thing we usually check is that Ole32.dll and OleAut32.dll are properly registered on both PC's.
To do this, go to the command prompt.
Tyep regsvr32 ole32.dll
A dialog box should appear saying: DllRegisterServer in ole32.dll succeeded.
Click OK.
Now type regsvr32 oleaut32.dll
A dialog box should appear saying: DllRegisterServer in oleaut32.dll succeeded.
Click OK and type exit to close the command prompt window.
Reboot and try to connect to the server again.
Remember these files need to be properly registerd on both PC's.
If that does not work then you can always go the rout of opening DCOM as wide as possible. Things to consider are as follows.
COM/DCOM, which is what OPC uses as a core technology, does not work well, and usually not at all, across multiple domains.
It is intended for use in Domains which have a central Access Control List. If you are using a WG(WorkGroup) or WG to Domain or Domain WG you need to make sure the OPC users in the Domain are built into the local security account of the WG PC(s).
To open security wide, which should only be done on a secure network, You need to have System and Everyone with Launch and access permissions on all PC's involved in the OPC connection. You should set this at the computer level and not the application level.
We have found that for reasons only known to Microsoft we sometimes need to set Local Securty Policies. Specifically we see a need to sometimes Enable "Network Access: Let everyone permissions apply to anonymous users" and set "Network Access: Sharing and Security Model for local accounts" to "classic - local users authenticate as themselves".
With recent Microsoft security patches we have seen in some cases a need to add Network Users for Access and Launch Permissions.
If you have a secure network you can also add Domain Admins and Domain users.
Once you have achieved an OPC connection and transfer of data between KepserverEx and you OPC clients you can then start to restrict DCOM permissions again.
If you have any further questions about using KepserverEx with OPC Clients you can contact [email protected]
Fred Loveless
Support Manager
Kepware Technologies
http://www.kepware.com
Fred Loveless
Kepware Technologies
http://www.kepware.com