mercedesP - 6:03 pm on Jan 12, 2011 (gmt 0)

Exactly the same here. WMT shows 404 crawl errors from several pages on my site pointing to "www.mysite.com/a".
In theory this was last updated on 21/11/2010.

I did all possible checkups to find that broken link, but it just doesn't exist and never has.
So, the only possible explanation is that there's a bug in G's end, as it's too much of a coincidence that the requested page is the same as meelosh's and aakk9999's.