I sure hope you have a backup of your encryption key.
http://support.microsoft.com/kb/290301
Clean up the omnipage install, then reboot and reinstall omnipage.
That might help
If it's not for WinXP, try this:
Go to Start/All Programs/Accesories/Program Compatibility Wizard. If you have the install on a CD, select the "use program on the CD Drive" option, or navigate there manually. Follow the wizard steps for the appropriate Windows release that your CD is designed for - Win 200, 98, 95, whatever.
Here is a solution I found on the web with people getting the same error message. Have you seen this?
You have to edit the Registry, and delete "PATCHES" 1. Regedit 2. click on Registry - Export and export the whole registry. 3. click on the Computer on the top so it searches the whole registry 4. Click Edit - Find and type in PATCHES ---- make sure you only look for KEYS 5. Rename all folders called patches to patchesold 6. press enter and F3 to continue searching. 7. NOTE: DO NOT RENAME APPPATCHES files. Dont touch them. 8. when done renaming the folders, install office 2000.