The 'Access-Control-Allow-Origin' header Contains Multiple Values '*, *', but only one is allowed. Origin 'http://sharepoint' is therefore not Allowed Access.

XMLHttpRequest cannot load http://MVCApi. The 'Access-Control-Allow-Origin' header contains multiple values '*, *', but only one is allowed. Origin 'http://sharepoint' is therefore not allowed access.
 
When such error arise, make sure to comment the below web.config entry under <system.webServer>.
  1. <httpProtocol>  
  2.    <customHeaders>  
  3.       <add name="Access-Control-Allow-Origin" value="*"/>  
  4.    </customHeaders>  
  5. </httpProtocol>