Well i was trying to add a site map in google webmaster and found an error saying the site map is unsupported but the site map was built in Wordpress with Google site map plugin
Did not meet that problem . I did it well . Is there any problem with the domain name ? Someone used it before ?
It may just not be in XML format. If you give a url to your sitemap it shouldn't be very hard to figure out the reason. you can also Google: validate Google sitemaps or something along those lines...there are a few sites that will help with validating a sitemap for the purposes of submitting them to Google.
whats the url ? you can use any free sitemap generator and upload that XML file in the root , your sitemap location should be - www. yourdomain. com/sitemap.xml