I think this is going to be quite difficult for someone else to resolve for you. The error message you are showing is complaining that the Certificate Authority (CA) is unknown. So there's something going on with the certificates needed to verify that the server is who it says it is. It's virtually a guarantee nobody has those files except the server administrator and hopefully you.
Certificate verify failed is basically OpenVPN saying that it has been instructed to verify that the certificate is the correct one. Usually this is done by providing a CA certificate to the client, and then when the client connects to the server, it takes the public certificate of the server, and holds it up against the CA certificate on the client side. If that shows that this server certificate was signed by this CA, then verification passes, and the connection continues.
In this case however it seems that you may not have (the right?) CA certificate. Nobody but the server administrator can provide that to you.
I do also want to point out that Windows 7 is out of support, and software isn't updated anymore for that OS. To rule out if it's because of outdated software that perhaps does not understand newer certificate algorithms and formats, you might try it on a more modern OS too just to rule that out as a cause. But I somewhat doubt that this is related to the OS, but more related to missing or incorrect files.
