Hello, this may be difficult to diagnose. The error is returned by the OPC server itself, and from previous experience, I would "guess" that it may happen when the OPC client wants to set up a notification callback in the OPC server, because this requires a "backwards" communication from the server to the client.
DCOM configuration advise:
support.softwaretoolbox.com/cg...
www.softwaretoolbox.com/xpsp2/...
<a href="
opcfoundation.org/DownloadFile.aspx?CM=3&RI=326&CU=1" target="_blank" rel="nofollow">
opcfoundation.org/DownloadFile...
Note that in case of IIS, the situation becomes more complicated. DCOM has to be configured for the client side (your app), but in this case your app is hosted by IIS. The IIS runs your application in a host process created by IIS. With some simplificaton, there usually is one such process per IIS AppPool. You should have a dedicated AppPool for applications that need DCOM, such as yours. If you do not have it, create it now. Select the identity of the AppPool so that it can access the OPC server. Still, you do not get a chance to configure DCOM for this process, so you need to rely on DCOM "default" settings that apply to the whole computer. For this reason, the instructions in the documents above only apply partially in case of IIS; whatever DCOM settings need to be done to the client app, now have to be done as default DCOM settings for the computer.
