Finally found the answer. It is because I remove my previous IIS and install IIS7. IIS needs to configuration of .NET library.
Run this command on cmd :
"%windir%\Microsoft.NET\Framework\"YOUR .NET VERSION"\aspnet_regiis.exe" -i
And then if your website's .NET version is lower than the version of your *.dll file , Change it from the application pool. After that it works well.