Not an "official" answer, but I've seen this problem before when you have an
additional version of Office installed. We have some employees that still
have to use Access 97 & have Office 03' installed. The track changes doesn't
work for them.
I've fixed a few of them with the following fix below posted elsewhere.
I found the problem and it was a registry issue, located at
HKEY_CURRENT_USER\Software\Microsoft\Office\11.0\Outlook\Journal, Item Log
file and Outlook Item Log file values were pointing to the wrong place. I
then changed the values to point to the correct locations then the Journal
started working.