matrix_jan - 9:16 pm on Oct 20, 2012 (gmt 0)
That's weird. My 404s went from 700-something to 9000-something in few hours because of bad programming. I received no messages. After few months I decided to turn 404s into 410s... It worked previously, so I hope it will work now too to remove those annoying errors from WM.
What I understood so far, 404 is a sensitive thing. If at some point somewhere was a link to it, even for few seconds(my case), then you should not let 404s to be there for a long time. If the page is gone return 410, if the url is incorrect 301 it, or just fix it if it's a technical thing. But don't let 404s to just stay there.
It confuses the bot, all it can understand is that it's not there, but what happened to it, is it gone, is it gonna come back, is it gonna redirect to something else?
So if at some point the bot visited a 404 page by following a link, then you should take actions.