Custom error redirects not working

Question

I'm trying to ensure that no non-standard error messages are sent to a user for security reasons. Generally I have standard error messages setup and it works perfectly fine. I use these tags in the web.config:

<httpErrors  errorMode="Custom">
  <remove statusCode="404" subStatusCode="-1"/>
  <remove statusCode="401" subStatusCode="-1"/>
  <remove statusCode="403" subStatusCode="-1"/>
  <remove statusCode="501" subStatusCode="-1"/>
  <remove statusCode="400" subStatusCode="-1"/>
  <remove statusCode="411" subStatusCode="-1"/>
  <error statusCode="403" path="/ErrorPages/UnAuthorized.aspx" responseMode="ExecuteURL"/>
  <error statusCode="404" path="/ErrorPages/Oops.aspx" responseMode="ExecuteURL"/>
  <error statusCode="501" path="/ErrorPages/Oops.aspx" responseMode="ExecuteURL"/>
  <error statusCode="400" path="/ErrorPages/Oops.aspx" responseMode="ExecuteURL"/>
  <error statusCode="411" path="/ErrorPages/Oops.aspx" responseMode="ExecuteURL"/>
  <error statusCode="400" path="/Account/Login.aspx" responseMode="ExecuteURL"/>
</httpErrors>

The problem I am having is it has been pointed out that some 403,400,501 error messages still don't get redirected.

The urls that cause this problem are:

www.example.com/con/ - asp.net error

wwww.example.com/..%5CStorage%5CDocuments%5C8849145d-174a-41ab-9676-0ae19d6ab741    - 403 error

and 411 errors from invalid content length.

Solution

Are you using VisualStudio Development Server or IIS7 Express? If you are using it then you should try with:

<customErrors mode="On" >
  <error statusCode="503" redirect="/Views/Shared/Error.htm"/>
</customErrors>

If not, try this:

<httpErrors existingResponse="Replace" defaultResponseMode="Redirect" errorMode="Custom">
  <remove statusCode="501"/>
  <error statusCode="501" responseMode="Redirect" path="/ErrorPages/Oops.aspx"/>          
 </httpErrors>