Ajax call - simple web service method returns entire page

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web

I have a simple function in my web service.

[WebMethod]
public string TryWB()
{
    string sMsg = "try";
    return sMsg;
}

and I am calling it from my aspx page. At the top I have tried

[ScriptMethod( ResponseFormat= ResponseFormat.Json)]

(or .xml or even httpget) and in the function also I have tried serialising it with

sMsg = (new JavaScriptSerializer()).Serialize(sMsg);

or even made custom object just to wrap message and even tried

JsonConvert.SerializeObject(cm,Newtonsoft.Json.Formatting.Indented);

From my aspx pages all combinations of text, xml, json made

$.ajax({
    URL: 'FLMSWebService/Login.asmx/TryWB',
    method:"POST", (get also tried)
    contentType: "application/json; charset=utf-8",
    dataType: "text",
    success: function (data) {
        alert('success');
        alert(JSON.stringify(data));
    },
    error: function (jqXHR, exception) {
        alert(jqXHR.responseText);
    }
});

I've tried: contentType: json, xml
and I've tried datatype : xml , json

I tried in web.config also

<system.webserver>
<modules>
<add name="ScriptModule" type="System.Web.Handlers.ScriptModule, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>

and

<system.web.extensions>
<scripting>
<webservices>
<authenticationService enabled="true" />

This is all I got from my 2 day search on net...but main point if I have

dataType: "text",

It's a success and full page returned as data in every other datatype or contenttype I get error and the full page is shown in

alert(jqXHR.responseText);

in the error callback. I am stuck!! please help

What I have tried:

in webservice method..

tried returning a simple string as it is or used JavaScriptSerializer
or xml format (created a simple string in xml format)
or object (in this case jsonconvert.serialize)
also used scriptmethod with all responseformats, even httpget tried

web.config file - ScriptModule added and webextensions added
in scriptmanager EnablePageMethods="true" added

and in .ajax(
datatype all tried json xml text (only ttext gives success but data is full page)
contentType: json, xml - tried