Having some weird crawl issues in Google Webmaster Tools

[Gordian]

I am having a large amount of errors in the not found section that are linked to old urls that haven't been used for 4 years. Some of the ulrs being linked to are not even in the structure that we used to use for urls. Never the less Google is saying they are now 404ing and there are hundreds of them. I know the best way to attack this is to 301 them, but I was wondering why all of these errors would be popping up. I cant find anything in the google index searching for the link in "" and in webmaster tools it shows unavailable as where these are being linked to from.

Any help would be awesome!

[Dan-Petrovic]

There are website crawlers you can employ to scan the site and hunt for specific parameters such as: http://home.snafu.de/tilman/xenulink.html