guys, wrote with permanent marker on electronic white board, now cant get it off. any tips please. i have tried going back over it with a dry marker and rubbing off-doesnt work. tried a little bit of alcohol- didnt work. tried a standard pencil eraser-worked a little bit but cant get it all off. any tips would be great as this item cost the school a lot of money and i would like to get it cleaned asap. many thanks for all your help.