Client Hyper-V in Windows 8 : Synthetic Ethernet Port: Failed to finish reserving resources

It turns out that my VMs somehow had two virtual ethernet adaptors, one of which was mapped to an adapter that had been removed from the "Virtual Switch Manager".

Right clicking on the settings, locating the second adaptor, then going to the right side of the screen and clicking the Remove button below the Network Adaptor's configurat properties list, solved the problem.

The error message could be better. Maybe it could say:

"You have two ethernet ports on this VM. Network adaptor #2, has an invalid configuration. Repair or remove the broken network adapter and try again."