Problem encountered

I am running Windows XP Pro.
 
I am the Webmaster for _www.sinaifreesynaggoue.org_ 
(http://www.sinaifreesynaggoue.org) .   When I validate the files that are on this Website, using I.E. 
6.0, I  get the response:
 
"This Page Is Valid _HTML 4.01_ 
(http://www.w3.org/TR/1999/REC-html401-19991224/)   Transitional!"
 
But when I validate the exact same files that are on my hard drive, I get  
the response:
 
 
"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).  
That you recieved this message can mean that your server is not configured  
correctly, that your file does not have the correct filename extension, or that 
 you are attempting to validate a file type that we do not support yet. In 
the  latter case you should let us know that you need us to support that content 
type  (please include all relevant details, including the URL to the 
standards  document defining the content type) using the instructions on the _Feedback 
Page_ (http://validator.w3.org/feedback.html) ." 
Are you aware of this problem and, if so, do you know why it's happening  and 
how it can be remedied? 
Thank you. 
Mitch