Usinf the CSS-Valdidator

Hello,

I try to use the submit file option to validate (X)HTML and CSS via a php 
script. Therefore I created a class which builds my HTTP-Request, open a socket, 
submit the request and read the answer. Works all fine with the xhtml 
validation, but i get an error when validating the CSS. The header I submit is 
the following. Could you please tell me why it does not work?
 >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
POST /css-validator/validator HTTP/1.0
Host: jigsaw.w3.org
Content-Type: multipart/form-data; 
boundary=accessibility_webEdition419c580188ee31100765185
Content-Length: 466

--accessibility_webEdition419c580188ee31100765185
Content-Disposition: form-data; name="file"; filename="dummy.html"
Content-Type: text/css

.error{
   color: red;
}

.success{
   color: green;
}
--accessibility_webEdition419c580188ee31100765185
Content-Disposition: form-data; name="usermedium"

all
--accessibility_webEdition419c580188ee31100765185
Content-Disposition: form-data; name="submit"

check
--accessibility_webEdition419c580188ee31100765185
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Received on Thursday, 18 November 2004 08:45:45 UTC