Even Anna Wintour can have trouble navigating the epic scrum of Fashion Week. Spies say that the Vogue editrix headed backstage before designer Scott Sternberg’s Band of Outsiders show when she was stopped by a clueless security guard Saturday at Sir Stage 37 on West 37th Street. He yelled, “Ma’am, you cannot come back here without a wristband!” But spies said Wintour returned to her seat to watch the show with guests including Simon Doonan and Lynn Yaeger. The night before, Wintour had arrived at Milk Studios for designer Billy Reid’s show, spies said, only to be told at check-in that the event wasn’t there at all. Wintour kept her cool. “Anna didn’t even respond,” said a spy. But Wintour made it to Eyebeam (the proper venue) in time for the show and was photographed chatting with Reid backstage. A Vogue rep had no comment.