Emilio,
I am glad this is resolved.

Actually, neither "Launching User" nor "Interactive User" are usually good settings for OPC servers. Except for rare scenarios, you should probably switch to a specific, pre-set user (I think the choice is marked "This account" or "Specific account" or similarly).

The reason for it is that with "Launching User", if there are multiple OPC clients configured with different identities, the system will attempt to start multiple instances of the OPC server, which, for most servers, won't work.

Best regards

The error indicates a problem setting up a callback mechanism. It has to do either with permissions and user accounts - either in DCOM configuration, or for/in the client application, or a combination of these. If things like node browsing, normal Reads and Writes work well, this error means that the "opposite to normal" direction has a security problem: The SERVER cannot access the CLIENT (for the callback mechanism).

There are, however, so many combinations of DCOM settings and other configuration items that I cannot provide a concise guidance. I suggest that you start by checking for setting differences (DCOMCNFG, user accounts) between the servers that work and server that don't work.

On the client side, you may try to change the settings at the bottom of this thread: www.opclabs.com/forum/connections-reconnections-com-dcom/124...achines-via-code-quickopc-dcom .

(and possibly, have a look at www.opclabs.com/forum/com-connections/1345-dcom-for-opc-configuration-tutorial#1796 , support.softwaretoolbox.com/app/answers/detail/a_id/1554 ).

Best regards

From: e...
Sent: Monday, July 14, 2014 10:59 AM
To: Zbynek Zahradnik
Subject: A technical question.

Hello Zbynek,

[...]

I noticed the following, which might cause problems if we do not find out where the reason is.

I made a small client application, standard EXE, to integrate some OPC Subscription, items subscribed from many different OPC servers.
Everything works fine.

Then I integrated the test implementation in the real application, which is a Windows Service (if that helps...it seems the only difference) and I noticed that for some OPC server only, not all, the OnValueChanged() event comes only once with the exception: "Access is denied".
For the same servers everything works fine in the test application, standard EXE.

Maybe you have seen already such issues, that is way I'm asking you before starting analysing here and there...

I can tell you more: because of policy restrictions (I have a laptop) I have to start VS2012 and each EXE that is itself a WCF Service for example (our Windows Service is also hosting a WCF Service) with Administrator rights.

Can you see some light???

Thanks in advance,

with my best regards,
E...