Yo también traté de hacer un cambio en mi página y me salió el mismo aviso. Quisiera saber cómo se resuelve esta situación.

Many former Page Creator users have received the same "hiccup" message on their Google Sites when they've tried to edit using Internet Explorer. But when they then tried a different browser (usually Mozilla Firefox or Google Chrome), their attempts at editing went more smoothly. Here's a link for more info