On Windows Server 2008 R2, a Hyper-V 2.0 guest may not recognize a change in the optical drive when you replace a disk.
Consider the following scenario:
On Windows Server 2008 R2, you install a Hyper-V guest operating system from Optical media.
The guest operating system finishes installing.
You eject the installation disk from the optical drive and replace it with another disk.
When you access the optical drive from the guest OS, Windows Explorer still shows the original install disk contents and will cause an error when you access it
For more information on this issue, including potential causes, workarounds, and resolutions, see: Microsoft KB Article KB2005143.