So MIDIYoke is a nice MIDI port patcher made back in the olden days. You might have trouble installing it on Windows 7. This is due to the new security features in Windows 7, the so called UAC.
So what you need to do is turn off UAC when installing MIDI Yoke. It goes something like this:
Go to the Control Panel -> System and Security -> Action Center -> and to the left you find the settings for the User Account Control. Set it to minimum and reboot. Install MIDI Yoke. Reboot again and reset the UAC to whatever tickles your fancy. It might be a good idea to have an administrator account while doing this.