SEO by Yoast doesn't work in the page editing panel?

Hi,

I’ve installed and activated WordPress SEO by Yoast and cannot seem to change or add anything to the Yoast tool located on the pages editing panel. I write for exampel a meta description and then update the page, but then the description disappears again.

I’ve heard that SEO doesn’t work when the current page has several revisions stored? In that case I like to erase old revisions, but cannot find a way to do it i Fruitful. Anyone who can help me out?

Thanks