After upgrading Windows, e.g from Windows 8.1 to Windows 10, some functions of Virtual CD will not work properly anymore, i.e. the license cannot be found anymore and you cannot insert a virtual CD.
After upgrading Windows, e.g from Windows 8.1 to Windows 10, Virtual CD has to be reinstalled in order to make sure that all functions are working properly.
Note: This also may pertain major updates within Windows 10, eg. the November update (version 1511)! As of version 11 this problem will not occurr anymore.
Please also observe the following KB article: Welche Virtual CD-Version unterstützt welches Betriebssystem?