I actually had the same problem. Now iWork '09 completely stopped working on my Macbook Pro...
Everytime I start any of the iWork Applications I get the following error code (in this case with Pages):
Process: Pages 
Path: /Applications/iWork '09/Pages.app/Contents/MacOS/Pages
Version: ??? (???)
Build Info: Pages-7660000~4
Code Type: X86 (Native)
Parent Process: launchd 
Date/Time: 2011-02-05 19:11:14.773 +0100
OS Version: Mac OS X 10.6.6 (10J567)
Report Version: 6
Interval Since Last Report: 711362 sec
Crashes Since Last Report: 18
Per-App Crashes Since Last Report: 11
Anonymous UUID: 855CBD3F-4E20-49EF-92B7-A4D161231332
Exception Type: EXC_BREAKPOINT (SIGTRAP)
Exception Codes: 0x0000000000000002, 0x0000000000000000
Crashed Thread: 0
Dyld Error Message:
Library not loaded: @rpath/Inventor.framework/Versions/C/Inventor
Referenced from: /Library/Application Support/iWork '09/Frameworks/SFCompatibility.framework/Versions/A/SFCompatibility
Reason: image not found
0x8fe00000 - 0x8fe4162b dyld 132.1 (???) <A4F6ADCC-6448-37B4-ED6C-ABB2CD06F448> /usr/lib/dyldMacbook Pro, Mac OS X (10.6.6)
Re-installing the app is usually the first step in such a problem. It often works, and often nothing else works, because the app has become corrupted. So, unless you have your disks, or at least proof of purchase (which may move Apple to give it to you again), you may be up a creek.
Other than that, you have a number of other things you could try: maintenance apps (OnyX, applejack, among others), real fixit apps (DiskWarrior, Drive Genius, TechTool Pro). If those didn't work, remove all prefs associated with iWork and its apps. Finally, re-apply the most recent OS combo updater.
If you had a backup of your system from a time when everything worked, that would, of course, be easiest, but I suspect you don't, or you wouldn't be here.
I wish you luck, but don't hold your breath.MBP, Mac OS X (10.6.6)
In my case, Keynote or Numbers would not open after a clean Mavericks install. The App Store showed Intalled and just could not figure out how to download again. The problem was that my external drive connected to the mac did contain very old keynote and numbers application files, hence making the app store I already had these, though they did not show in my home applications folder... I deleted those from the external usb drive, re-opened the App Store, et voilá! installed and worked right away, like a charm, like everything Apple! Thanks!