Implementing a Custom Error page on an ASP.Net website

Try this way, almost same.. but that's what I did, and working.

<configuration>    <system.web>       <customErrors mode="On" defaultRedirect="apperror.aspx">          <error statusCode="404" redirect="404.aspx" />          <error statusCode="500" redirect="500.aspx" />       </customErrors>    </system.web></configuration> 

or try to change the 404 error page from IIS settings, if required urgently.

There are 2 ways to configure custom error pages for ASP.NET sites:

1. Internet Information Services (IIS) Manager (the GUI)
2. web.config file

This article explains how to do each:

• How To Set Up Custom Error Pages In IIS 7.5 With ASP.NET

The reason your error.aspx page is not displaying might be because you have an error in your web.config. Try this instead:

<configuration>   <system.web>      <customErrors defaultRedirect="error.aspx" mode="RemoteOnly">         <error statusCode="404" redirect="error.aspx"/>      </customErrors>   </system.web></configuration>

You might need to make sure that Error Pages in IIS Manager - Feature Delegation is set to Read/Write:

Also, this answer may help you configure the web.config file:

• What is the difference between customErrors and httpErrors?

<customErrors defaultRedirect="~/404.aspx" mode="On">    <error statusCode="404" redirect="~/404.aspx"/></customErrors>

Code above is only for "Page Not Found Error-404" if file extension is known(.html,.aspx etc)

Beside it you also have set Customer Errors for extension not known or not correct as

.aspwx or .vivaldo. You have to add httperrors settings in web.config

<httpErrors  errorMode="Custom">        <error statusCode="404" prefixLanguageFilePath="" path="/404.aspx"         responseMode="Redirect" /></httpErrors><modules runAllManagedModulesForAllRequests="true"/>

it must be inside the <system.webServer> </system.webServer>