Sorry to hear this.
Did you already contact Apple Care?
Interested to see what they replied to you.
They advised me to reinstall Keynote and test with another user.
Did this but quite time consuming. Test user didn't fail ...yet. Regular user failed again after reinstall.
Does the same occur to PowerPoint for Mac? (if you installed it)
iWork has to be removed completely to be effective when re-installing, you must use an application removal tool to do this or it wont remove every Keynote file.
Appcleaner will do this and its free.
The following procedure has helped solve many issues with Keynote:
1 Close Keynote then use Appcleaner
2 Empty the Trash
3 Shut down the Mac, then restart and press the shift key immediately after the startup sound, then release shift when the Apple logo appears
allow the Mac to boot up to the desktop, it will take longer then usual as the hard drive is being repaired
4 restart the Mac
5 Reinstall iWork
6 Repair permissions:
Applications > Utilities > Disk Utility > First Aid: click on your system disc in the drive column
and select Repair Disk Permissions
7 open Keynote and test
Post back to let us know if this was successful.