Because of a problem with SP3's wbemoc.inf, a custom cab package was created containing updated versions of wbemoc.inf. If the SOURCE folder contains Windows XP SP3 or if it is to be updated to SP3, HFSLIP won't continue if wbemoc.cab is not present in HFCABS.
You can read more on the wbemoc.inf issue and others involving Service Pack 3 on this new page on the HFSLIP site. The new page is also accessible from the Guidelines section in the main navigation menu on the HFSLIP site ("Windows XP SP3" link).
The Basic how-to and Downloads pages were updated as well.