I'm trying to train Ninjutsu and can't attack my Mirror Images to get rid of them, so I can cast more. I'm currently in the low 50's. The guide says to cast, kill and repeat but I have to just wait til I have less than 5 before I can cast another. Please help advice. When I try to attack one of the images it says "that is forbidden" I tried being in and out of a guild and in tram and fel, guard and no guard zone.