How to set up custom errors for an ASP.NET application

ASP.NET has its own built-in error handling. To set up custom error handling for your ASP.NET application, you will need to modify your web.config file.
For example, if you want to redirect all 404 errors to error404.aspx, 500 errors to error500.aspx, and all other errors to error.htm, you would update the customErrors element in your web.config as follows:
<customErrors mode="On" defaultRedirect="error.htm">
  <error statusCode="500" redirect="error500.aspx"/>
  <error statusCode="404" redirect="error404.aspx"/>
CustomErrors are off by default. If you do not customize the custom error element in the web.config file, the default ASP.NET error (with debug information) will be displayed.