Hello,
we already have some user reporting the same or similar problem, and it is unclear where it is coming from. It probably has to do with accessing the client application certificate that QuickOPC creates automatically for OPC UA communications.
I can only guess that things got somehow mixed in the certificate stores. Can you please try the steps described further below.
1. Download, install and run (with elevated privileges) the UA Configuration Tool, from
www.opclabs.com/products/ua-configuration-tool .
2. Switch to the Manage Certificates tab.
3. Verify that you have ".... UA Appplications" in the Store Path field.
4. Press View Certificates.
5. Locate any certificate that look "yours". Their name will be based on the name of the EasyOPC UA Demo executable, or whatever is the name of the app that has the issue. Select each such certificate, right-click on it, select Delete, and confirm. If you do not have other UA apps on your computer to be concerned about, you can delete all certificate that you see. When done, press OK.
6. click on the drop-down next to "Store Path", and select "... Machine Default".
7. Repeat steps 4 and 5 on the Machine Default store.
8. Close the UA Configuration Tool.
Then, try to run the demo app again. Make sure you it - at least the first time - with elevated (admin) privileges. They are usually needed to store new certs into the certificate stores.
This may help - let me know about the outcome. If it doesn't, we will try further.
Best regards