Thank you for your answer. So let me clarify a bit more. The problem is that the customer is encountering has been resolved by following your guidance in this post:

www.opclabs.com/forum/quickopc-ua18/2243-impossible-to-conne...op-server-in-same-network#9032

Now, you stated "When an application based on OPC Data Client auto-generates its application certificate, it places it into both stores. This allows other applications based on UA .NET Framework SDK residing on the same machine immediately trust it." - but I do not believe that is the case in some "random" cases. Is this due to permissions? I am not sure.

In this case, the customer had to follow our instructions based on the blog post above because the certificate was not stored in both paths. Basically, the certificate was never stored in the "UA Applications" path but it was in the MachineDefault path. I am trying to understand why this is happening in some systems, but in other systems, we can find the cert stored in both paths.

Hello Z,

Currently, I am working with a customer who encountered the error:

OPC-UA service result - Self Signed Certificate is not trusted.
IssuerName: CN=EasyOPC-UA Demo, DC=kubernetes.docker.internal = BadCertificateUntrusted.
---- SERVICE RESULT ----
Status Code: {BadCertificateUntrusted} = 0x801A0000 (2149187584)
-=-=-Description: Self Signed Certificate is not trusted.
IssuerName: CN=EasyOPC-UA Demo, DC=kubernetes.docker.internal
Additional Info: <ExceptionTrace>

Now, we know that the issue is that this is not an issue with the OPC UA Client trusting the OPC UA Server certificate, but rather the OPC UA Client's certificate being in the correct Certificate Store on the machine. We also know that the code used in the OPC Data Client from the OPC Foundation requires the Client application certificate to be present in the Trusted Peers Certificate Store, which in this case is %CommonApplicationData%\OPC Foundation\CertificateStores\UA Applications.

Now, I am curious, and I was hoping you can provide me with an answer or perhaps point me on the right path - Do you know what determines where that certificate is executed by default? In other words, do you know why in some machines the certificate is in the "MachineDefault" path, and on other machines, it is in the "UA Applications" path?

Now, to remedy this, should I be able to just use this exampleexample to always force the certificate to be executed in UA Application path?

Thank you in advance.