Ajax goes to error with status = 0, but Fiddler returns 200 -

here's code:

$.ajax({             type: "post",             async: true,             url: "/mycontroller/mymethod",             data: {                 items: grid.getallrowids()             },             success: function (data) {                 debugger;                                 },             error: function (a, b, c) {                 debugger;             }         }); 

the parameters correct because method in controller entered, ajax doesn't go success. goes error instead, status code = 0. fiddler says ok.

what going on?

and response text empty string.