Jessica Simpson's voice wasn't ready to perform live but she decided to give it a go anyway. She sang "I Belong To Me" pn the Today Show and was unable to complete the song without her voice giving out on her.

Jessica Simpson sang for the first time since injuring a vocal cord a week ago, but only made it through one song before her voice cracked.
Simpson croaked her way through "I Belong to Me" on NBC's "Today" show Friday morning, but when it came time to hit a high note on "With You," her voice cracked. She paused for a moment and said, "All right, I tried that one," before finishing the tune.
"That had to be the most nerve-racking thing you've ever done in your life," said "Today" co-host Matt Lauer. (source)

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