Hi Guys,
You may faced this issue before.
The network connection of a running Hyper-V virtual machine is lost under heavy outgoing network traffic on a Windows Server 2008 R2-based computer.
Description: This affects all guest operating systems. The fix is applied to the hypervisor and while a reboot is required for installation, no updated need to be applied to the guest operating systems.
Here is the HotFix >>
http://support.microsoft.com/kb/974909Give it a try!