jquery ajax call is working in ie but not working google chrome,firefox,safari

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ASP.NET

jQuery

webservice

Hello,

i have struggled with one problem.
ajax call with jquery for webservice working fine in ie but not working in googlechrome, firefox,safari.

in googlechrome,safari and firefox it gives response as undefined

this is my code..

in aspx page

$.ajax({
                type: "POST",
                url: "xxx.svc/logindetails",
                contentType: "application/json",
                data: '{ "UserName": "' + UserName + '","Password": "' + Password + '"}',
                async: false,
                success: function (data) {
                    if (data.text == '') {
                       // xxxxxxxxx  
                    }
                    else{//redirect}
},
                error: function (data) {
                    //alert();
                }
            });

in xxx.svc:

OperationContract]
        [WebInvoke(Method = "POST",
            BodyStyle = WebMessageBodyStyle.WrappedRequest,
            ResponseFormat = WebMessageFormat.Xml
        )]
public string GetUserDetailsbyLogIn(string UserName, string Password)
        {
string msg="";
// checking user exist or not
           return msg;
}

anyone can know about this pls help me
thanks in advance...