Webmaster Tools shows 1 URL error (not found page).

The report says that 5 pages are linking to a page (let's call it x) that does not exist (and because it doesn't exists it returns a soft 404). HOWEVER, I look in those 5 pages (in the source code) and none is linking to the x page. It is like Google sees an old page that was indeed pointing to x.

What is the problem? How do I know if Google cached an old version for those 5 pages?