Problem with executing asp.net program

Thanks for your answer but this problem occurs when I create a website. When I create a webapplication, this problem does not exist.

Hi majid,

 When we run any webapplication then a development webserver starts and host the page for temporarily. I think you webserver is not installed or its services is stopped. 
If you are using the Visual Studio then this server used to run the webapplication is known as Cassini Development server. find the issues regarding this.

Here are few article for similar problems:
http://www.mcse.ms/message2302693.html
Setting up the cassini server:
http://www.ultidev.com/products/Cassini/CassiniDevGuide.htm

Thanks.