PageMethods Is Undefined ASP.NET AJAX

If you are getting PageMethods Is Undefined Error while using AJAX in ASP.NET or using a webservice than you need to check these things to resolve the issue

1. PageMethods needs to be static

[WebMethod]
public static int MethodName()
{
}

2. Enable pageMethods in scriptManager

<asp:ScriptManager ID="ScriptManager1" runat="server" 
                   EnablePageMethods="true">
</asp:ScriptManager>

3. add reference to script service in code behind
Add [Microsoft.Web.Script.Services.ScriptMethod] or [System.Web.Script.Services.ScriptService] in code behind below [WebMethod]

WebMethod] 
[Microsoft.Web.Script.Services.ScriptMethod]
public static string GetRecords()  
{  
//DO something  
}

Hope this helps