I have a Mac Mini which runs a virtual Mac OS machine on top of the normal Mac OS. This was very fine for Mac OS 10.11, and 10.12 but fails on Mac OS 10.13. My setup is MacOS 10.12.6 as the host OS and Parallels 13.1.1 (43120). Inside Parallels, there is one guest machine running MacOS 10.12.6, which I want to upgrade to 10.13. When I start the upgrade process of the guest OS machine, the machine is shut down and reboots. At reboot, I get a strange sign instead of the apple logo that look like a "no stopping" traffic sign. After a while, the machine boots into Recovery HD and I can select to start the original version of 10.12.6 but no upgrade is progressing. What is wrong here?