Compressor serial number invalid Issues.
If you ever have problems with compressor telling you your serial number is invalid make sure you completely uninstall it then reinstall it. It’s a little more complicated than just trashing the application and removing the preference files. Compressor is linked to Qmaster and hold its serial information in files you might not know about.
Apple has on their website some “Compressor: Troubleshooting Basics” that will tell you how to properly uninstall compressor here.
Of course doing everything they say on their site is a pain and can take awhile. So I found this program the other day that does a great job or properly uninstalling all of the Final Cut Studio apps. So if you ever want to roll back your final cut version or change serial numbers for whatever reason check out this app here.
It will remove all preference files and delete whatever final cut app you want automatically. Better than app zapper or any other program designed to remove apps.
NOTE: Make sure you repair your Disk Permissions in your Disk Utility after you do all this and before reinstalling FCP or Compressor.
Be sure to check out their website http://www.digitalrebellion.com/ for some other awesome tools for dealing with Final Cut’s failures to work properly and its annoying bugs.
Hope this helps and fixes your issues with compressors serial number being invalid or not working properly for whatever reason.