Problem (duplicate url ):submit sitemap to google webmaster with wordpress

Hi to all of my friEnd ! when i am chatting in my blogger group then we seen a common error or problem in webmaster tools while we submit our sitemap (which contribute for promote or publishing our site) and that's problem is the "DUPLICATE URL:This URL is a duplicate of another URL in the sitemap. Please remove it and resubmit”.
my close friend sumit jha(blogger) also faced with that problem then i tried for resolve that and 1st go for Webmaster forum but i didn't get help much clearly then i tried my best and i got it......
You have to aware about that webmaster tools google but all such as yahoo,bing,msn for submit your sitemap for indexing your blog on web search results.Now come on the topic about the problem,which you seen like that..

But don’t worry. It is occurring for the Xml-Sitemap generator plugin. After posting any new post in your blog, the plugin generates the sitemap for your site and updates the notification to Google, yahoo,bing, ask.com etc. But if you add the URLl manually then the problem creates. The problem may be created for any other reasons

To solve this problem you have to drop the duplicate urls from your sitemap. So download the Sitemap.xml file from your root directory and remove the duplicate URLs manually and upload it again. But if the volume of your blog is too large then it is not so easy to remove the duplicate URLs manually. Don’t worry, go to your root directory where the site belongs. It should be /yoursite.com/. Now take a backup of your Sitemap.xml and Sitemap.xml.gz and delete those from your root directory. Now go to your dashboard and open Xml-sitemap plugin under settings menu. Delete all the entry if you added manually (no need to add URL manually, if your site folder in the root directory Sitemap generator will do it automatically) and press“Rebuild the sitemap manually”. Go to webmaster tool and resubmit the Sitemap. Wait for some days. You will see the result soon. Don’t panic for your indexed URLs. Google will show the exact no of URLs that was indexed before.