ajax call cannot be completed with 1.7 version

Question

When I try to call ajax using jquery 1.5/1.7 it gives an error "No transport" (the same jquery works fine with 1.3). To avoid this I tried using "datatype" parameter with the $.ajax function as "JSONP"(datatype:jsonp). The "No transport" error is gone and a call goes to the webserver and is executed properly but it again gives error (may be parsererror) saying "jqueryxxxxx was not called". Below is what I used:

$.ajax({ url: WebServiceUrl + "/" + MethodName,
        data: "profileName=amol&IsSyncRequired=false",
        contentType: "application/x-www-form-urlencoded",
        dataType: "jsonp",
        jsonp: "jsonp",
        complete: function(jqXhr, status) {
            alert('result1');
            if (status == "timeout" || status == 'parsererror') {
                jqXhr.abort();
            }
        },
        success: function(result) {
            alert('result');
        },
        error: function(xhr, ajaxOptions, thrownError) {
            alert(xhr.status); alert(thrownError);
            alert(xhr.responseText);
        }
    });