After BootCamp Import: "no boot device is available"

Hi everybody
I have a problem with my Parallels installation or with a VM:
after a long time I decided to import the existing BootCamp installation into Parallels. I have created a new VM via file import from BootCamp according to the instructions. This went through as far as it could, but now when I start the VM I get the message that no operating system is installed.
What do I have to do to get the Windows installation running again?

Parallels Desktop: Version 14.1.3 (45485)
mac Os High Sierra, 10.13.6 (17G14042)

With best thanks in advance
Rik