Two things to try:
1 - Test to see if the theme is corrupt:
start a new bank presentation and recreate a basic version of the presentation, containing three to five slides, using the same shapes fonts and effects - do not use the theme or any items from the theme that was supplied to you.
If that test works it points to the theme file being corrupt, ask for another copy of the theme and test, if that does not work recreate the theme your self
2 - reset Keynote to discover if the application is corrupt, complete all of the steps in the order listed:
1. ensure you have a current backup of all your user files saved to a separate drive
2. close all applications
3. uninstall Keynote; for this procedure to work, an application removal tool must be used, App Delete has a free trial and works for this procedure. It can be downloaded from the developer’s website here: App Delete
4. empty the Trash (Finder > Empty Trash)
5. restart the Mac (Apple Menu > Restart) Immediately after the Apple bong sound, press the shift key on the keyboard, release shift when the Apple icon appears. Start up will take longer than usual as the Mac is performing a software repair of the start up drive.
6. After the Mac is fully powered up, restart the Mac normally: Apple Menu > Restart
7. reinstall Keynote from the Mac App Store in the Applications folder
8. Restart the Mac again
