The Orlando Sentinel had more details. The Lizzie McGuire series on the Disney Channel was ending anyway, and they offered her a new series on ABC. She made $15,000 an episode on the Disney Channel and they offered her $35,000 per episode for the ABC series. She wanted $100,000 per episode. They couldn't agree on a figure and so the series idea was scrapped.
They also offered her a Lizzie McGuire sequel. She asked for $4 million and they agreed. They also agreed to give her a bonus of $500,000 if the first movie made $50 million. It looked like it was good, then her negotiators demanded the bonus no matter how the first movie fared. Once again, they couldn't agree and so the movie deal was also scrapped.