AJAX call not working when async: true - asp.net

Question

So I want this AJAX-call to run asynchronously but it only works with async: false
var url = 'Default.aspx/CheckLogin';
$.ajax({
async: true, // works with async: false
type: "POST",
contentType: "application/json; charset=utf-8",
url: url,
data: '{"email":"' + email.val().trim() + '", "password":"' + password.val().trim() + '"}',
dataType: "json",
success: function (data) {
alert("success!");
},
error: function (result,something,error) {
alert("Error: " + error);
}
});
EDIT:
When async is true the alert will show immediately with "Error:", that is no error msg.
The CheckLogin function is pretty slow so when it actually runs it it takes a while.
Any idea of what I'm doing wrong?
EDIT 2:
This is some info I got from chrome://net-internals/#events:
t=1381258516496 [st= 0] +REQUEST_ALIVE [dt=12]
t=1381258516497 [st= 1] +URL_REQUEST_START_JOB [dt=11]
--> load_flags = 142737665 (ENABLE_LOAD_TIMING | MAYBE_USER_GESTURE | REPORT_RAW_HEADERS | VALIDATE_CACHE | VERIFY_EV_CERT)
--> method = "POST"
--> priority = 2
--> upload_id = "0"
--> url = "http://localhost:1176/web_new/Default.aspx/CheckLogin"
t=1381258516497 [st= 1] HTTP_CACHE_GET_BACKEND [dt=0]
t=1381258516497 [st= 1] +HTTP_STREAM_REQUEST [dt=11]
t=1381258516508 [st=12] CANCELLED
t=1381258516508 [st=12] -HTTP_STREAM_REQUEST
t=1381258516508 [st=12] -URL_REQUEST_START_JOB
--> net_error = -3 (ERR_ABORTED)
t=1381258516508 [st=12] -REQUEST_ALIVE

Answer 1

Async true is the default for ajax. There are times when you need to set it to false, for example, you might make another ajax call inside your callback , in that case, you will need to set outer ajax call to async false and the one in the callback to true.
Also, since your making a call to a code behind, make sure to format your data correctly and the codebehind webmethod is static. Other than that, your ajax looks ok.