you probably have a wear ridge on the inside edge of the drum which hooks round the shoes preventing removal,sometimes you can give the adjuster a small tweak with a screwdriver to knock it off a wee bit through the back plate but dont know on this model,make sure the h/brake cable is let off completely and sometimes you just have to persevere with a couple of levers until it removes,sometimes it pulls off the shoe retaining springs and clips so be prepared for that and when the drum is off get a grinder and buff off that wear ridge and next time you shouldnt have the same problem,good luck
wickham
October 2010