Important if you follow these Steps you loose nothing, don´t delete any VM´s only remove Fusion App self !!!
many many Problems in Sierra and High Sierra coms from Gatekeeper Process so if you get Errors starting your VM´s or
some other Errors please do following:
1 Remove Fusion from your Mac
2 Download a new Copy of Fusion 10x .dmg
3 open a terminal go to your download folder like cd Users/YourUserName/Downloads
3 past that in your Terminal
xattr -dr com.apple.quarantine
don't hit enter !! now go to finder and to your Download folder grab the Fusion dmg file and drag and drop it to your Terminal Windows
you will get something like that:
xattr -dr com.apple.quarantine /Users/YOURUSERNAME/Downloads/Fusionxxxxx.dmg
IMPORTANT there must be a space between xattr -dr com.apple.quarantine and the Rest !
now hit enter and if promt is back open that dmg and try a fresh install.
If that solve your Problem you can stop the Gatekeeper with thais command but be aware you will break your Mac Security a little bit !!:
defaults write com.apple.LaunchServices LSQuarantine -bool NO
If that Solution works for you than your hole Problems are the Gatekeeper process, this process stores every downloaded file to quarantine
normally it should com out of quarantine if the app was in Applications Folder but some times that do not work and than hole App or part of the app
goes in quarantine than you get some strange Error Messages and mostly the App stop working
I hope my English was not so bad and everybody understand what i mean