BillyS - 12:13 pm on May 8, 2010 (gmt 0)
Again if I understand Dusky correctly he is saying that if using that url the page resolves and doesnt throw up a 404 page not found error, then potentially you have duplicate content issues.
Back in late 2005, early 2006 duplicate content of this type was a big problem. Many of us took steps back then to eliminate these problems at that time.
If you're using a CMS like Joomla or Wordpress, they've solved this issue by now either in core or through an extension / module.
Google Webmaster Central has some useful information on creating custom 404 pages.