There are two things I would try:
First, download and apply the BITS patch from Microsoft (available here: http://www.microsoft.com/downloads/details.aspx?FamilyID=b93356b1-ba43-480f-983d-eb19368f9047&DisplayLang=en) – sorry about the long URL, blame Microsoft…
This is KB842773.
If that doesn’t work, break out your original install media (the Windows 2000 install CD if possible) and run a repair. You’ll have to re-apply service packs and security updates, so try the KB842773 route first….