New VM on Windows 7 Virtual PC cannot access host's DVD Drive

New VM on Windows 7 Virtual PC cannot access host's DVD Drive

"I have a brand new clean machine with Windows 7 Professional 64bit and I've installed the patch that adds Windows Virtual PC (Windows6.1-KB958559-x64).
I then go to Windows Virtual PC, create a new Virtual Machine. As soon as go to settings and try to map the VM DVD drive to the host's DVD drive I get ""File may be in use by another process or you may not have sufficient access privilege"".
I am an administrator in that box..."