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Why I am getting the error "Class Not Registered" when I try to connect to OPC server situated on another machine using OPC client.

The error you are getting because Citect's OPC client requires registry settings to be present on the client machine for the OPC servers that you want to connect to.

Now export the registry settings on the OPC Server PC to *.reg files. For each OPC Server you will find below three branches in the HKEY_CLASSES_ROOT tree of the registry.

- HKEY_CLASSES_ROOT\<ProgID of OPC Server>
- HKEY_CLASSES_ROOT\CLSID\<CLSID of OPC Server>
- HKEY_CLASSES_ROOT\AppID\<AppID of OPC Server>

Just select the desired branch, right click and select option export. (Registry | Export Registry File). The CLSID can be found in the ProgID branch, the AppID can be found in the CLSID branch of the OPC Server.

Second step is run those .reg files, which you just created, on the client machine (Citect Machine). Just double click on the .reg file and the desired registry entries are automatically updated on client.

Another method for getting the right settings, is simply installing the OPC server on the client machine. Some OPC Servers already have exported the registry settings to a small executable or a .reg file, in that case just run that file.
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