We always see different error message from the browser. There are four kinds of error pages listed as below. Here I will clarify which kind of error message will be returned under different configuration.
1. Custom page
2. IIS error info
3. ASP.NET error info
4. Hide detailed error
The <httpErrors> element allows you to configure custom error messages for your Web site or application from IIS level. Custom error messages let you provide a friendly or a more informative response by serving a file, returning another resource, or redirecting to a URL when visitors to your site cannot access the content they requested. Please refer to http://www.iis.net/configreference/system.webserver/httperrors
customErrors is the configuration at the ASP.NET level. Please refer to http://msdn.microsoft.com/en-us/library/h0hfz6fc(v=vs.100).aspx
Custom error only focus on if the detailed error message returned from asp.net. If custom error is set to off, we will not see the detailed asp.net errorinfo.
Httperrors focus on if returns the custom error info or return the detailed error info. The existing mode focus on if returns the iis error info or asp.net error info. The 54 kinds of combinations is listed as below for your reference.
Charles Liang from GBSD DSI Team