BITS and System Restore
Not all versions of BITS use the same format to store jobs. If you return the computer to a restore point prior to a BITS upgrade, the old version of BITS may not be able to read the current job information. If this happens, BITS will delete the jobs list and create a new empty jobs list. As a result, the temporary files associated with the previous jobs list are not cleaned up; to reclaim the disk space, you must delete the files manually.
Users familiar with the Windows command line can avoid this problem by using the BITSAdmin tool (found on the Windows CD in the Support Tools directory) to clear the BITS jobs list before running System Restore. To clear the BITS jobs list, run the following command:
bitsadmin /reset /allusers
Note that you must have administrator privileges to run this command.