just got this issue fix on friday, turns out my problem was with the task scheduler.
here's my fix might be worth a try on your site.
1. Remove the MP as a site system role (if it is still installed), wait for it to finish
2. Run a ccmclean /all (this is a tool you can find in the SMS 2003 Toolkit 2)
3. Remove IIS completely
4. Reboot
5. Stop the Task Scheduler Service
6. Rename the %windir%\Tasks folder to something else (or move it)
7. Start the Task Scheduler Service (this will recreate the %windir%\Tasks folder)
8. Optional: Enable auditing on the \inetpub\wwwroot folder (and subfolders). Make sure to set local security policy to trap failures of file access. We will need this in case we see the same security failure.
9. Reinstall IIS, BITS, WebDAV
10. Insure BITS and WebDAV are enabled
11. Reinstall the MP