No "Access-Control-Allow-Origin" header is present - asp.net-web-api

Question

I have put the parameter in the web.config of the web.api that is being called. I even put it in the webapiconfig.cs to allow all sites hit the web.api. Even put it on the controller. And I still get this message? The calling website is sending json over to my web api. Why would I , could I be getting this error? What information can I give you guys to help me figure out this issue?
In reply to the solutions listed below: Here is the piece of my web.config....I put the wildcard of asterisk in it:
<httpProtocol>
<customHeaders>
<add name="Access-Control-Allow-Origin" value="*" />
<add name="Access-Control-Allow-Methods" value="*"/>
<add name="Access-Control-Allow-Headers" value="*" />
</customHeaders>
</httpProtocol>
Within my webapiconfig.cs file I have the following as well:
{
// enable CORS
config.EnableCors(new EnableCorsAttribute("*", "*", "*", "*"));
}
And here is my controller. I know, overkill, but I am trying to figure out this issue:
[EnableCors(origins: "*", headers: "*", methods: "*")]
public class ExampleController : ApiController

Answer 1

Just check your web.config file and search for system.webServer section:
<system.webServer>
<httpProtocol>
<customHeaders>
<remove name="Access-Control-Allow-Origin" />
<remove name="Access-Control-Allow-Headers" />
<add name="Access-Control-Allow-Headers" value="Origin,X-Requested-With,Content-Type,Accept" />
</customHeaders>
</httpProtocol>
</system.webServer>

Answer 2

Try reading through https://developer.mozilla.org/en-US/docs/Web/HTTP/Access_control_CORS for the general idea of what's going on, and http://www.asp.net/web-api/overview/security/enabling-cross-origin-requests-in-web-api for how to solve it in ASP.net
Essentially, if your request is coming from one server to another on a different domain, the other server must say it's happy to accept requests from browsers on the first domain.
To fix it, tell ASP.net to return 'Access-Control-Allow-Origin' headers that include the origin your request is coming from, either via web.config (as in the other answer), or by adding to your config and controller classes as below:
public static class WebApiConfig
{
public static void Register(HttpConfiguration config)
{
config.EnableCors();
// ...
}
}
namespace WebService.Controllers
{
[EnableCors(origins: "http://myclientdomain.azurewebsites.net", headers: "*", methods: "*")]
public class TestController : ApiController
{
// ...
}
}