lucy24 - 8:01 am on Dec 6, 2011 (gmt 0)
This is potentially two different questions.
#1 You know that 404 errors exist, because you've found them via GWT or similar. Now you want to find out where these bad links are coming from in the first place. Wander through the Forums and you may conclude that much of the time it isn't worth the trouble.*
#2 You want to know whether your site is drawing 404 errors.
Unless you've got an unspeakably complicated site, you need not worry about internal bad links. A quick run with the link checker of your choice will turn up any problems.
* I just took a quick detour to gwt. The latest "not found" is
404 (Not found), ostensibly linked from "1 pages". (Um, g###, have you any idea how easy it is to code that to make it grammatical?) That one page(s) turns out to be some everything-but-the-kitchen-sink site that I've never heard of. Oh, I am so going to seek them out and make them fix the link. Yeah. You betcha. Especially since my page-- minus the "CachedYou"-- doesn't even have any content that belongs in that kitchen sink.