I don't see why google would complain about that. That just means you have 3 friendly urls all resolving to the same page. The actual site map you submit to google webmaster tools should be this url: http://www.whybaptist.com/SiteMap.ashx and there is no duplicate there.
What message is google giving you? Do they provide any links to more details about the problem?
The one being used in the menu and site map is http://www.whybaptist.com/1forestsstudy.aspx, I think you could safely delete the other friendly urls from the url manager, but I wonder if you have linked to that page somewhere in your content using one of the other urls. Google may see that when it crawls your site, but it is not seeing duplicates in your site map, because those other 2 urls are not in the site map.
Hope it helps,
Joe