Thanks for your fast reply.
I have uninstalled Fusion 5.0.3, reinstalled Fusion 6.0.0 and changed the Hardware Version from 10 to 9.
Version 9 ist accepted for Fusion 5.
After Uninstall Fusion 6 and reinstall Fusion 5 I get the same error message as before: "You must reduce the Compatiblity of the Virtual Machine".
What´s the matter? Have I to reduce to hardware version 8, it is also suitable for Fusion 5?