The Most Wanted singer is adamantly denying rumors she wasn't all there during a stop on her 2008 Dignity tour in Monterrey, Mexico, this weekend, after footage of the concert, in which she appears to be mouthing words into a microphone, made the Internet rounds.

"She was not lip-synching," Duff's rep said in a statement confirmed by E! News. "It was faulty equipment. There was no sound coming out, but she was singing." They were relying on locally provided equipment during Saturday's show, the rep said. - more on this story

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