If you are using .net web api and again and again you build your's project and run that you will see that your's runs on different port after running you will be get following error in console window

Error: No ‘Access-Control-Allow-Origin’ Header is Present – Origin ‘localhost:…’ is therefore not allowed access.

this is very comman issue which can stuck  the developer in web api 

you can remove this by just configure the Global.asax file in Application_BeginRequest section  

by the following code in which we just configure the header section of the service

protected void Application_BeginRequest(object sender, EventArgs e){

HttpContext.Current.Response.AddHeader("Access-Control-Allow-Origin","*"")

}