Today I run in to the problem where I could not remove a Hyper-V Hosts from System Center Virtual Machine Manager. The Hyper-V host was reinstalled before he was removed from SCVMM and the host was showing has HOSTNAME (pending) in the SCVMM Management Console. If you did a right click to remove the host, the Remove option was greyed out.
But don’t worry Windows PowerShell came to the rescue, with the following command you can remove the Hyper-V host from Virtual Machine Manager.
Get-SCVMHost <HOSTNAME> | Remove-SCVMHost -force