SonicWALL blocking random sites.

My school uses SonicWALL on their internet network and it continually blocks sites as hacking proxy. When I check the current rating to request a re-rate it comes up with an accurate rating, but whenever I actually go to the sites they get blocked. Some friends who have macs have no problem accessing these same sites . Are some of my computer settings screwing things up or something? Why is SonicWALL blocking things for me and not others?