I see Google Crawl 404 Errors (Not Found) for Category, Archive, and Author related URL's. With the example below it shows 2 Pages, the adjacent pages, linking in to the one not found:
Page Not Found - http://blog.thehigheredcio.com/category/cio-job/page/23/
Linked From Page - http://blog.thehigheredcio.com/category/cio-job/page/24/
Linked From Page - http://blog.thehigheredcio.com/category/cio-job/page/22/
Although most of these occurrences are when the Linked From page appears to be the last page and the Not Found page would be the next Older Posts page. But several of the Linked From pages are also Not Found.
Reading Settings >>> Blog pages show at most = 10
Reading Settings >>> Syndication feeds show the most recent = 5
I have seen other Support Forum threads discussing mismatches in the showpost query value but I cannot locate it to determine if this is the issue.