I have made more tests, in an attempt to reproduce the remaining problem. The tests used two newly installed computers (client side + server side). On the client side, I was using both QuickOPC, and Softing OPC Client. I have tested many different security configurations, and in all cases but one, the results of QuickOPC and Softing OPC Client were the same - i.e. they either both worked fine, or none have worked.
There was one configuration under which the Softing OPC Client was able to enumerate the OPC servers on the remote computer, but QuickOPC not. I have investigated the problem in this case, and fixed it in QuickOPC. It is not precisely equal to your situation, however, because it only affected the browsing for OPC servers, but not the actual connection to the remote OPC server. Due to the code logic, however, I can foresee that it actually could be the same thing you are experiencing.
When you get a chance, can you please download the recent build from our Web site (5.12.1205 or later), and retest?
Best regards

Thanks again for the information. Unfortunately I cannot reproduce the problem currently, with the latest version sent. I will try to set up a different, separate environment for it. This will be after January 2, though.
Best regards

Just to be absolutely sure:
Start the "EasyOPC Options" utility, and on the System Parameters tab, uncheck the box for "Module Parameters -> COM security -> Turn off call security" (i.e. this time, turn this setting off), and press OK.
The "Use custom security" box should be checked (on).
And make sure the EasyOPC process is restarted.
Many thanks

Dear Sir,
thank you very much for the new information and the analyzer trace. I have reviewed the errors contained in the trace file. I suggest that you (once again) download and try the very recent of the software (this time it is 5.12.523.1 or later). This is not "shooting in the dark" - in fact we have recently had very similar issue reported by another customer, and there is a supposed fix contained in this latest version.
Best regards

If this has not helped, please do this:
Run the DCOMCNFG utility (on Windows 7, just press the Start menu button, and type DCOMCFG into the box; may be different on other systems, let me know if you need help). From the Console Root, select Component Services -> Computers -> My Computer. Right-click on "My Computer" and select Properties. In the dialog, select the Default Properties tab, and change the Default Authentication Level to None (the Default Impersonation Level should be Identify).
Hope this helps.

Thank you. This is indeed helpful. Please do the following:
Start the "EasyOPC Options" utility, and on the System Parameters tab, check the box for "Module Parameters -> COM security -> Turn off call security" (i.e. turn this setting on), and press OK. Make sure that the EasyOPC process is shut down so that it gets a chance to pick up this new setting, and then perform your test again. Hopefully it will resolve the problem. If not, even if the symptoms do not change, please grab another trace using the Analyzer and post it again.
Best regards,