Fixing the 404.3 HTTP Error: A Complete Guide

Fixing the 404.3 HTTP Error: A Complete Guide

There are various types of errors users can come across when visiting or navigating a website. While its frustrating for the visitors, its panicking for the admin and website owners. One of the most common errors is the HTTP Error 404.3 – Not Found error.

The main reason behind this error is non-existence of MIME mapping or script handlers in the IIS web server. In this article, learn how to fix this error.

What the 404.3 HTTP Error Means?

An HTTP error occurs when the server doesn’t serve the requested web page. The HTTP error come with a status code, which informs what exactly went wrong.

404 errors indicate that the reason for non-delivery of the web page is unknown. 404.3 is a sub status code and sheds more light on the reasons. When you get the 404.3 error, you should know that there’s a MIME restriction. You can confirm this by going through the error message, which reads something like this:

HTTP Error 404.3 – Not Found

The page you are requesting cannot be served because of the extension configuration. If the page is a script, add a handler. If the file should be downloaded, add a MIME map

As you can see, the requested page is a script and the handler needed for it is missing. If the images or videos are not loading, then the required MIME-type is not available. The error can also surface if ASP.NET feature is not enabled.

The error usually occurs among websites hosted on a Windows and IIS web server.

Fixing the Error

There are a few ways you can fix this error. Here are three recommended solutions to try:
  • Install ASP.NET feature
One of the reasons behind the error is ASP.NET feature is not enabled. This also means, ASP.NET is not installed. So install it first. Here are the steps to follow:
  • Go to Start >> Administrative Tools >> Server Manager
  • Locate and click on Add roles and features
  • Select features and then expand .NET framework
  • Select the required ASP.NET framework. Once you select the ISAPI Filters, other parameters like ISAPI Extensions, .NET Extensibility will be selected automatically
  • Next, you run the following commands on Windows architecture:
◦    %windir%\Microsoft.NET\Framework\v4.0(framework version)\aspnet_regiis.exe -ir (For 32bit (x86) Windows)
◦    %windir%\Microsoft.NET\Framework64\v4.0(framework version)\aspnet_regiis.exe -ir (For 64bit (x64) Windows)
Lastly, verify that the application pool of the domain is using the framework.
  • Adding a Script Handler
Majority of the websites use PHP and .NET to function. The webserver must have the necessary script handler to handle these languages. If not, you’re sure to see the 404.3 error. Here are the steps you need to take:
  • Open Internet Information Services (IIS) Manager
  • Go to Home > Server Components
  • Select Handler Mapping
  • In the Action pane, locate and click on Add Module Mapping
  • When the dialog box opens, provide the following details:
Requested path: *.php
Module: FastCgiModule
Executable: “C:[Path to PHP installation]\php-cgi.exe”
Name: PHP via FastCGI
  • Click on OK to close the dialog box
  • Check the PHP info page. It should list the FastCGI module details
It should fix the 404.3 HTTP error.
  • Select MIME-type
The third way to fix this error is to select the correct MIME or Multipurpose Internet Mail Extensions type. The primary role of MIME is to identify the type of content served to the browser.

The IIS server might have already installed MIME-type on your server by default for files like HTML and jpeg. But for newer content types, the MIME-type might not have been installed. So follow the steps to do that:
  • Open the IIS Manager
  • In the Connections panel, you need to select the site/directory/application where you need the required MIME type
  • Next, in the Home panel, double-click on the MIME Types option. It’ll list all the default MIME-types
  • Click on Add to add the required MIME-types to the list
Now, restart the IIS. The problem should have been resolved now that there is a MIME-type to handle the script type.

So that’s how you deal with the 404.3 HTTP Error. For more assistance, contact the support team.
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