you must have a link somewhere in your site that points to that page. when you say "google" do you mean that you get this error in the webmasters tool? if so then it should mention which page it found the broken link on.
for the sitemap generator, i don't know which one you are using (maybe you can post it in the thread) but usually they just spider through your site. i went to your url http://fdomains.net/ and it looks lie a board, so if anyone posts a url it might show up when you try to get a sitemap done depending on the sitemap generator.
I'm sure you could make a rewrite rule for this and do a 301 redirect to lets say the root but do that only if you cant find the link.
Yea it said it found it at fdomains.net/ wich is my index page. BUT I do not see that link anywhere.