Just reinstalling iWork ´09, and/or deleting the plist file did not work. What did the trick was to follow the steps that Jerry recommended:
1. Use OnyX to purge caches and repair permissions for a general maintenance of your system.
2. Use Yvan Koenig's iWork '09 uninstaller script to wipe all traces of iWork and it's ancilliary files from your system. Find it on this page.
3. Reinstall iWork.