cannot start Hyper-V virtual machine

Hi,

I have a Windows 2008 Server. It has been now upgraded to Windows 2012. Everything was working fine. But, now I turned off the virtual machine and copied the VHD file to another drive for backup. After this, I am not able to start the old virtual machine. (The VHDs are in place. I only copied them) However, two another virtual machines are running now without any problem. While trying to start, I am getting the error "the operation cannot be performed while the object is in its current state". These are critical server. Any quick thoughts?

Thanks

Tom Jacob