Parallels Desktop displays the following error message during your virtual machine upgrade:
Manual interaction is required to complete the configuring of the \\"%1\\" virtual machine.
The upgrade could not be completed automatically, because some operations in Windows require your attention.
Please switch to manual upgrade mode by pressing Ctrl+Command+Alt+R keys simultaneously and when prompted, hit "Yes".
You will see the pop up notice/message that is hiding behind the upgrade screen. Complete the action required (depending on the Windows message) and the upgrade will continue automatically.