"Connection Timed Out. Description: Connection Timed Out." Error

Question

I do my project with VS 2012,ASP.net web form project, LinQToSQL, the lastest Ajaxtoolkit and using session. When I pusblish my project to server and sometime I click on link in my web then click any buttons on page the Web Browser shows the error:

"Connection Timed Out

Description: Connection Timed Out."

I don't know how to fix it. What cause this problem and how to fix it? Here is my web config :

<add name="Database_ConnectionString" connectionString="Data Source=.;Initial Catalog=MYDatabase;User ID=sa;Password=1234567;Connection Timeout=30"
      providerName="System.Data.SqlClient" />

<httpRuntime targetFramework="4.5" maxRequestLength="20480" enable="true" executionTimeout="110"/>

<sessionState timeout="60" mode="InProc" cookieless="AutoDetect"       regenerateExpiredSessionId="true" useHostingIdentity="true">
      <providers>
        <add name="DefaultSessionProvider" type="System.Web.Providers.DefaultSessionStateProvider, System.Web.Providers, Version=1.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" connectionStringName="DefaultConnection"/>
      </providers>
    </sessionState>

Please help me. I will die soon with this problem.

Thank you so much.