I had the same problem.
How is this the same problem?
The original post was regarding continuing to use an expired trial version of Keynote which obviously wont work after the trial has expired.
Otherwise I would recommend this maintenance procedure to re-instate Keynote:
1
Uninstall all of iWork if you have this, otherwise uninstall Keynote on its own if other iWork applications are not installed.
This must be done with an application remover to delete the installation properly. Appcleaner is known to work correctly for this purpose, it is free and can be downloaded from here: Appcleaner Download
2
empty the trash
3
shutdown the Mac and restart. After the start up chime, hold down the shift key until the apple logo appears
let the Mac complete the start up procedure completely, it will take longer than usual as the software installation on the hard drive is being repaired
4
go to; Applications > Utilities > Disc Utility > First Aid > Repair Disc Permissions
when this is completed restart the Mac normally
5
Reinstall iWork or Keynote as appropriate using the original method on purchase, using the installer file or install from the App Store.