First things first..run a windows update on the machine then run an office update on the machine and see if this fixes the problem. If you have already done this we will take it to the next step.
If that dont work I recall trying a few other things to fix this on a clients machine. One was to edit the registry, one was to apply some form tool update and another deleting some type of file...but make sure you run that office update for the latest service packs and updates.