Britney Spears by Kevin Mazur/ Britney Spears by Kevin Mazur/

What's the real story behind Britney's unfortunate "Oops!" at Sunday's VMAs? ( Watch video here.) As sources weigh in, a recurring theme suggests that a last-minute change in plans - perhaps not at all helped by frozen margaritas - led to the pop tart's onstage bewilderment. TV's Extra, for one, hears that a more elaborate number orchestrated by illusionist Criss Angel was pared down just before the show got under way. It would not have been an entirely insurmountable hurdle if Spears had hit rehearsals hard. Instead, a source tells the New York Daily News, "She showed up three and a half hours late, and she walked in with a frozen margarita. It was so disrespectful." Not just to MTV suits and her fans, but to her fellow dancers as well. "The dance number was spectacular - without her," a spy tells the New York Post. "Then Britney showed up and refused to do anything. The more complicated moves had to be erased."

Wardrobe-wise, Spears has taken hits for underdressing, a questionable choice made by herself when she deemed a corset designed to go with the sparkly bra and bottoms "not sexy enough," says the Post.

Is this Britney's worst year ever? Opportunistic VH1 answers that question with a (preplanned) special that airs Tuesday night.

UPDATE: In honor of Ms. Spears' "return," has given its Britney page a glam makeover (albeit sans holey fishnets). Check it out!