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?
The only thing you can do is use the site operator in Google search for the URL and then view the cached copy of the page to see how old it is.
site:http://example.com.comI really wouldn't worry though, 404's are normal on the internet and most websites will have some, as long as you're happy they aren't linking to those non existent pages any longer then just concentrate on more worthwhile matters.
I saw something similar in my GWMT reports some time ago, many 404 or 500 errors from URL's not linked from a page. I find out GoogleBot takes everything that looks like an URL and makes requests to it. Take a look at your javascript or html, look for anything that looks like an url and compare them to those urls reported as broken.
