Windows 8 has many drawbacks.
Not only removing Midi mapper but also:

In dosbox, when I installed Sound blaster 1.5 in windows 3.1 adlib appear in devices. I restart windows, and I am trying to play midi files until it says "The current Midi Mapper setup refers to a midi device that is not installed on the system. Use MIDI mapper to edit the setup." Adlib supposed to be in emulator but strangely windows 3.1 did not detect them after I installed adlib. I tried to remove and re install it, restarted it, trying to play a midi file, same problem occurs. And I also tried to remove and reinstall windows, restarted it, reinstalled soundblaster 1.5 and adlib appears in devices, i tried to play midi file, same problem goes again. If i do removed the adlib, restarted it, reinstalled it, restarted it, and I tried to play midi file, same problem goes again once more.

Please help me! Thanks!