some of the highjackers create a .dll file on the boot which reside in the windows/system directory that cannot be deleted as they are active in memory when windows is running. If your scan can't delete it it will at least identify the file. Then boot to DOS prompt and delete the offending .dll file manually. Make sure you make a copy of file beforehand & renaming it something like filename.old instead of filename.dll so it won't be activated on the boot.... just in case it's not the right file, or if it has an unforseen impact, you can rename it back.