making multiple ajax/jsonp requests doesnt seems to work!

making multiple ajax/jsonp requests doesnt seems to work!

I am using the following code to make multiple requests 
  2. var a1 = makeRequest(config.servers[0]);
  3. var a2 = makeRequest(config.servers[0]);
  4. var all=[a1,a2];
  6. $.when(all).done(function(results) {
  7. console.log(results);
  8. });

  10. function makeRequest(server) {
  11. return $.ajax({
  12. url: buildUrl(server),
  13.         type: "GET",
  14.         dataType: 'jsonp',
  15.         jsonpCallback: "datasource "
  16.      });
  17. }
Intermittently I am getting the following error! Why?
  1. Uncaught TypeError: datasource is not a function