Validation by file upload and Internet Explorer on WinXP SP2

From September 2004 to February 2005, a bug in Windows XP Service Pack 2 (SP2) was breaking the "validation by file upload" feature of the W3C Markup Validator when used on browser "Internet Explorer". The bug was reportedly fixed by the Windows security updates released in February 2005. We encourage validator users still experiencing the problem to update their system.

This page is kept here as an archive for the fixes, workarounds and information on the issue.

Working around this issue

(updated 2005-02-09) With the release of Windows updates meant to fix the issue, the most simple solution should be to apply the security updates, especially MS05-014.

If the above does not work, here are a few other possible workarounds:

A simple solution is to use a different browser. The Validator's file upload mechanism is reported to work normally with most, if not all browsers (except Internet Explorer), even on WinXP SP2.
Alternatively, publishing the document to validate on the Web and publishing by URL also works.

Information on the issue

Typical symptoms

The typical symptom was the following error message, received when trying to validate a .html file via file upload:

Sorry, I am unable to validate this document because its content type is text/plain, which is not currently supported by this service.

The Content-Type field is sent by your web server (or web browser if you use the file upload interface) and depends on its configuration. Commonly, web servers will have a mapping of filename extensions (such as ".html") to MIME Content-Type values (such as text/html).

Causes and History of the issue

An entry in our bug and issue database is where we tracked and discussed technical details as well as the evolution of the issue up to its resolution.