As you suggessted, I changed it to have only sitemap.xml as shown below. But nothing has changed. Still, there are 4 HTML (400 errors), 8 In Sitemap (404 errors), 14 Not Found (404 errors). And, all of these error links are working when I click on them.
User-agent: *
Disallow: /aspnet_client/
Disallow: /Bin/
Disallow: /App_Code/
Disallow: /Common/
Allow: /*
Sitemap: [ External links are visible to forum administrators only ]
Thank you for all your help.