url not found by google

[autogearbid]

I get this msg in my google webmaster tools area regarding my sitemap:

Web crawl errors 
HTTP errors  0  -- 
Not found  11788  Details » 
URLs not followed  9  Details » 
URLs restricted by robots.txt  0  -- 
URLs timed out  0  -- 
Unreachable URLs  13  Details » 
Total:  11810 

When I go into the (Not found) page it lists all links that where not found. I click on one of the links at random, When I click the link the link is dead.

[external links are visible to admins only]

Why the aitemap crawling old pages deleted from my site? Can this be the prob??

[admin]

Hello,

"Web crawl errors" report is located in a separate section of webmaster account and is not related to sitemaps.
Is this URL included in the sitemap?