I too am getting errors in my sitemaps where it says I have 404 errors on pages that don't even exist.
You are not alone.
I believe that Google takes these URLs not from your sites and not only from the scrappers' sites but also from the browsers address bar and similar direct requests.
Just one way how Google may do this As you know in the Google Toolbar there is the option "make Google default search engine". If someone enter a wrong URL Google tries to find it, in other words the wrong direct request comes to the Google. There are probably other ways, for example some options in the Google analytics.
In my case the 401 URL's are attempts to check my sites, probably by hackers. One URL would have been correct if not the affiliate ID at the end. I never have been using the affiliate id's. Other url also almost correct but has aspx at the end. Aspx is the page extension of the Windows server but my host uses Lynx. So theses are clear attempt to check my site. Google detects them.