Weird Google Crawl Errors

I'm getting thousands of crawl errors from Google such as.............

http://conservativetalkforums.com/~r/retort/~4/DGJJHI5Q48g	404 (Not found)	unavailable	Jul 14, 2011
http://conservativetalkforums.com/~r/retort/~4/428XvsW9GvQ	404 (Not found)	unavailable	Jul 14, 2011
http://conservativetalkforums.com/blog/gunrunner-justice-department-tampering-with-witnesses/	404 (Not found)	unavailable	Jul 14, 2011
http://conservativetalkforums.com/2011/07/the_speech_boehner_should_give.html	404 (Not found)	unavailable	Jul 14, 2011
http://conservativetalkforums.com/2011/07/betty_fords_civility.html	404 (Not found)	unavailable	Jul 14, 2011
http://conservativetalkforums.com/news/milwaukee/125027704.html	404 (Not found)	unavailable	Jul 14, 2011
http://conservativetalkforums.com/article/journalist-detained-for-photographing-courthouse-seeks-answers	404 (Not found)	unavailable	Jul 14, 2011
http://conservativetalkforums.com/article/another-photographer-detained-in-southern-california	404 (Not found)	unavailable	Jul 14, 2011
http://conservativetalkforums.com/staff/stephen-dinan/

There are no such URL's as /~r/ or /blog/ or /news/ or /article/. Where is it picking up such non-existent locations?

Those are just warnings.

returning a 404 is the correct thing to do since these don't exist.

Google will follow bad links (such as people linking to external pages and forgetting the http so it ends up like http://www.yoursite.com/someothersitefolder/page/) and even 'stuff' urls to try.