I had come across this issue when I try to add the Hyper-V 2012 Core to VMM 2012 SP1,

Warning (26179)
Couldn’t enable multi path i/o for known storage arrays on host BS-SITS-HV12
Enable multi path i/o for storage arrays being used on host manually after adding multi path feature.

Import-Module ServerManager

Add-WindowsFeature Multipath-IO



If you get any error when you try to add 2012 Core to VMM 2012 sp1, install the File Server role in the, it will fix your issue.

type: powershell in the prompt;

PS C:\>Install-WindowsFeature FS-Fileserver