Javascript – Web Service method name is not valid

I get the following error "Web Service method name is not valid" when i try to call webmethod from javascript

System.InvalidOperationException: SaveBOAT Web Service method name is not valid.
at System.Web.Services.Protocols.HttpServerProtocol.Initialize()
at System.Web.Services.Protocols.ServerProtocol.SetContext(Type type, HttpContext context, HttpRequest request, HttpResponse response)
at System.Web.Services.Protocols.ServerProtocolFactory.Create(Type type, HttpContext context, HttpRequest request, HttpResponse response, Boolean& abortProcessing)

HTML Code :

<asp:LinkButton runat="server" ID="lnkAddBoat" OnClientClick="javascript:AddMyBoat(); return false;"></asp:LinkButton>

JS Code :

function AddMyBoat() {
            var b = document.getElementById('HdnControlId').value;

            jQuery.ajax({
                type: "GET",
                url: "/AllService.asmx/SaveBOAT",
                data: { Pid: b },
                contentType: "application/text",
                dataType: "text",
                success: function(dd) {
                    alert('Success' + dd);
                },
                error: function(dd) {
                    alert('There is error' + dd.responseText);
                }
            });
}

C# Code (Web method in AllService.asmx file)

[WebMethod]
public static string SaveBOAT(int Pid)
{
    // My Code is here
    //I can put anythng here
    SessionManager.MemberID = Pid;
    return "";
}

I tried all solutions found on Stack Overflow and ASP.NET site.but none of them worked for me.