MTV bosses have pleaded with pop star Britney Spears to "behave" at Sundays (09Sep07) Video Music Awards, according to reports. The Toxic singer confirmed an appearance at the ceremony on Thursday (06Sep07). MTV bosses announced the troubled star would make her live music comeback onstage at the event with a performance of Gimme More, the first single from her upcoming fifth album. But Spears has allegedly been warned if she fails to behave appropriately in the run-up to the VMAs, her performance will be pulled from the show. A source tells the New York Daily News, "Britney knows she's on thin ice. When they agreed to the performance, they sat her down and told her she should not be going out, and instead focus on rehearsing and resting. "She seemed to be thankful and appreciative for the chance, but who knows her? MTV made it clear her usual behaviour will not be tolerated." Despite being spotted partying in Las Vegas earlier this week (ends09Sep07), her cousin Ali Simms insists Spears is taking her VMA performance seriously. Simms says, "Her performance will be huge. She's very excited."