Which version/build of FinalBuilder are you using? I made some changes to work around that issue late last year. This build from today has those changes included :
FWIW, the changes were to add a slight delay after deleting a sub folder before attempting to delete the parent folder. It seems the windows api doesn’t keep up with itself when deleting folders recursively. This also started happening more often with later XP updates, I never did figure out which update caused the problem though… far too many to test!