I recently upgraded my Mac to OS X El Capitan 10.11.6, version 9 does not work. So I downloaded version 10 and use the version 9 activate code but it's not being accepted. Do I need to buy version 10?
Yes, you are right. Only Parallels Desktop 10, 11 and 12 support Mac OS X El Capitan. You may purchase the full copy of Parallels Desktop 12 from Parallels Online Store and if you would like to buy Parallels Desktop 10 and 11, please check if it is offered by your local resellers or authorized online resellers.