Office 2010 will not display its own help files

I'm running Office 2010 on Windows XP SP3. Whenever I try to ask for help, it pops up a dialog box that says:

There is a problem with one or more installed help files. Please repair your Office installation and try again.

I tried repairing the installation; no luck.

I tried renaming c:\Documents and Settings\All Users\Application Data\Microsoft Help and repairing the installation. Office created a new version of that folder and populated it. Office still won't display its help files.

If I log in as a different user, it works, which means there's something weird about my user profile.

It works fine on my other computer, which as far as I know is configured similarly.

Any idea how I can find out what Office doesn't like about my user profile? I've seen the suggestion elsewhere that the way to solve this problem is to create a brand new user profile, copy all your stuff over to it, and use that instead. I really, really don't want to do that because of the number of unknown other things it is sure to screw up.