Starting VMs that try to share DVD drive

This was an odd one…

I created a new VM on my Hyper-V host. The VM would not start. It turns out that I had two VMs on this Host both trying to use the hosts DVD drive as its own. This doesn’t work.

Found a description and the solution here.

Moral of the story: Make sure an ‘off’ VM is not trying to use the DVD drive if it is already assigned to an ‘on’ VM.