Error: Could not load file or assembly 'AjaxContolToolKit'? Strong name signature could not be verified?

I had formatted my disk fully and then reinstalled the windows. After reinstalling i had opened my project and run it. then it gave me this error.

Could not load file or assembly 'AjaxControlToolkit' or one of its dependencies. Strong name signature could not be verified. The assembly may have been tampered with, or it was delay signed but not fully signed with the correct private key. (Exception from HRESULT: 0x80131045)

There is blue underline under first line of text.

<%@ Master Language="C#" AutoEventWireup="true" CodeFile="MainMaster.master.cs" Inherits="MainMaster" %>

How to resolve this error

You can find the solution here. Best choice to solve this issue would be to delete the dll and re upload a new one in your project.