If you are solving a problem with a non-functional OPC client under Win7 (the Channel properties do not show the available OPC servers on the computer in the window, with other clients, eg Matrikon Explorer, non-functional): install OPC Core Components V3.00. Download after registration here.
In Win7, the OPC client must be run as an administrator.
If, after installation and configuration, the OPC server is visible in the client, but you cannot connect to it, or after trying to connect, it connects for a few seconds and then disconnects, check if the parameters for connecting to the PLC (IP address, name, password, port, platform) have been saved in the configuration file. Configuration programs may have write access to the Program files (x86) directory disabled, the configuration will be saved in Program Data - and the original one will be loaded at the next start.
It will help to install the OPC server in another directory - e.g. c:\Apps\, where applications can write.
