If you already have OpenVPN installed and it is connected, then you will get the error that all TAP-Windows adapters are in-use. You cannot run VPNs that use the OpenVPN client simultaneously with IVPN. You have to make sure that they are not connected. One of those other VPNs is more than likely occupying the TAP-adapter whether it is connected or not. You'll have to troubleshoot. Having multiple VPNs installed on a system is a recipe for issues.