Bob Comer directed me to this post from the Virtual PC Guy's Blog but, before trying the recipes in the post (which involved logging out or restarting the system), I simply tried the Reset Folders option in the View tab of the Folder Options. And it immediately solved the problem.
So, if you are having this same problem, you might want to try this simple solution first.
In the end, just in case, I also added start menu shortcuts to:
- Windows Virtual PC Wizard
- Windows Virtual PC Settings