Whitney Houston had to cut back her park concert because of technical difficulties with her voice. Her excuse? Says the Daily News:

Whitney Houston cut short her much-hyped comeback performance on “Good Morning America” Tuesday after apparently losing her voice.
The Grammy-winning diva got through just three songs from her new album “I Look to You” before apologizing to the 5,000-person crowd for overusing her famous pipes.
“I’m so sorry. I did ‘Oprah.’ I’ve been talking for so long. … I talked so much, my voice,” she said, trailing off.

Right. And this is the woman who was supposed to have the undefeatable voice - who ironically "lost" her voice during her comeback concert.