You don't upload your sitemap to Google Tools. You give their site the url of your sitemap and upload the sitemap to your site. Let's start off with the url of your site, the sitemap in question and the specific error that you are receiving please.
Place your sitemap.xml in the root of your web (i.e. Upload it to your web host and place in the root of your web). My guess is that THIS is possibly the step you skipped. Verify that the file is there by requesting http://www.example.com/sitemap.xml with your browser to see if your sitemap is actually accessible by the engines (replacing www.example.com with your domain). You should see the XML displayed in your browser. Log into Google's WMT. Select your site from your WMT Home page. Expand the '+' next to Site Configuration in the Dashboard in the left sidebar. Click on Sitemaps under the Site Configuration sub-menu. Click on the Submit a Sitemap button. Enter the name of the sitemap.xml into the text box displayed after the URL shown for your home page. Press the Submit Sitemap button. You're done. If Google doesn't like your sitemap.xml they will give you a list of errors. They are usually self explanitory.
That's what I did. I submited then it shows this error I understand that in the "Privacy" section at my wp admin panel was marked to block search engines but now I changed to allow search engine's robots to access my site and still wont load the sitemap. It's weird because I use the same SEO wp plugin in my other blogs and it works perfectly.
good news... suddenly, after 500 resubmitions Google decided to access my sitemap! woohoo! thanks guys anyway!