deadsea - 12:48 pm on Sep 13, 2012 (gmt 0)

They changed it a while ago such that if there are no errors, that particular error type doesn't show up. (I can't find the blog post where the announced it, but I remember reading it.) My site only has tabs for "Not Found" and "Other". It currently doesn't have a tab that shows internal server errors.

That being said, I don't think I've ever seen a site with no 404 errors. Google seems to make up pages to query even once you have taken care of all the broken links. Right now they are reporting as 404 on my site things like "123456/ad_slot_top_main" which are strings used by the Google adserver and embedded in javascript. Certainly not urls. Just braindead crawl behavior.