Parallels Desktop 9 - Failed to open the Parallels networking module. After OS X El Capitan Install
Unfortunately Parallels Desktop 9 doesn't officially support El Capitan. I've received two Service Notification emails from Parallels which state:


  If you intend to upgrade to Mac OS X El Capitan (10.11), please note that Parallels Desktop 9 for Mac will NOT support OS X El Capitan (10.11).
  
  Before you upgrade to OS X El Capitan, be sure to upgrade to Parallels Desktop 11 for Mac. It is our latest version, fully optimized and enhanced for OS X El Capitan.


(From past experience, I usually have to upgrade Parallels Desktop every second OS X release. I'm currently on Parallels 9, am thinking of upgrading to El Capitan and came across this question when trying to research if I really do need to pay to upgrade Parallels. Unfortunately it appears I do...)