OpenVPN installation: unable to install TUN/TAP driver. Exit code 2

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http://serverfault.com – I downloaded the latest version of OpenVPN (msi). Compatible mode does not work because it is msi file, not exe. I do not know version number of openvpm because there is no such on the official web-site (http://openvpn.net/) and not any number in msi file. Windows 7 Ultimate x86. (HowTos)