Web.config Custom Errors mode Conflict

Question

I have a great and important problem with Web.Config, I need to see the Error of my page and resolve it in asp.net web form and web config, but when Error Occurred, I see an

Answer 1

Set the mode to On, save the web.config then refresh or restart the IIS and make sure the mode is still set to On after saved. Browse to it again, it should show the error...