You must be running the latest build of Parallels Desktop 8 before upgrading to OS X Mavericks. Click Parallels Desktop Menu >Check for Гpdates to install the latest build and proceed with upgrading to Mavericks. If you have already upgraded to Mavericks and your Parallels Desktop 8 doesn’t start, please download the latest build at http://www.parallels.com/directdownload/pd8