Those are security Torx screws from what i can see, chances are the ones you have aren't up to spec to fit on them what with the center hole not always being perfectly centered on them. You could try seeing what Torx size it is and see where the hole in your bit is.
You need a security Torx bit for it, which if the T8 you have is too large sounds like you'll need a T6 or T7. They're pretty cheap if you get junk ones for single use, but i'd recommend getting the slightly more expensive ones to make sure they hold up.