failing validation

Hallo,
  I have a problem with validation of my local files. I am not sure what is wrong because I have never received error messages like this before. One day it was OK but next day it was not possible to validate. I receive this informations: 
   
  Sorry, I am unable to validate this document because its content type is application/octet-stream, 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). 
   
  The extensions of my files are PHP. But it has never been a problem with this before. But when I walidate a HTML file on the same location, it works. 
  When I validate my web page (the same files) on line on the internet, it works even with PHP extensions.
   
  So please, can you give me any advice what to do???
   
  Thank you
  Milan (Czech Rep., Europe)
   
   
   
  So can you please give me some 

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