Could not create type 'FirstService',while accessing webservice

I have created web application called SampleWebservice,inside that I have added one webservice called FirstService.When I run on localhost it works fine

Folder Structure is

SampleWebservice folder : SampleWebservice sln file
SampleWebservice folder : Bin
:Obj
:FirstService.asmx
:FirstService.asmx.cs
Firstservice class had namespace SampleWebservice
My FirstService.asmx contain :
<%@ WebService Language="C#" CodeBehind="FirstService.asmx.cs" Class="SampleWebservice.FirstService" %>
I converted web application to virtual directory by clicking property of it. I am able to to see my virtual dirctory from IIS,from content view if I click on browse ,working fine

Url : http://localhost/SampleWebservice/FirstService.asmx
I want to add this SampleWebservice folder

SampleWebservice folder : Bin
:Obj
:FirstService.asmx
:FirstService.asmx.cs
to another folder named MainWebsite.I have copied SampleWebservice folder to MainWebsite folder.Here I get exception

I was trying url like this : http://localhost/MainWebsite/SampleWebservice/FirstService.asmx so I removed namespace from FirstService class as well as asmx file

still not working so again modified

<%@ WebService Language="C#" CodeBehind="~/FirstService.asmx.cs" Class="FirstService" %>
<%@ WebService Language="C#" CodeBehind="MainWebsite/FirstService.asmx.cs" Class="FirstService" %> Nothing worked out for me.No success.How to handle this?