This is usually caused by having different versions of Office installed at
various times on your computer. To resolve this problem:
Run Office Setup and uninstall Office
Navigate to Program Files and delete the folder Microsoft Office
Open the registry editor - start, run and type in regedit
Find HKEY_CURRENT_USER/Software/microsoft/ and delete the key "office"
Find HKEY_LOCAL_MACHINE/Software/microsoft/ delete "office".
Close the registry editor and reboot.
Reinstall Office