Dear Juergen, According to our licensing policy, an upgrade to Parallels Desktop 11 for Mac is supported from the following versions only: Parallels Desktop 9 for Mac Parallels Desktop 9 for Mac Upgrade Parallels Desktop 10 for Mac Parallels Desktop 10 for Mac Upgrade If your previous version key is for Parallels Desktop 8 or earlier, please visit the Parallels Online Store to purchase a full license for Parallels Desktop 11 for Mac: http://www.parallels.com/store/ Please refer to this article to activate Parallels Desktop 11 for Mac.