OAuth request token problem

[Luis]

Hi, i have a django site with some models exposed trought piston, i'm
trying to implement oauth but i hitting a mayor roadblock with this.

i'm trying to comsume the service trought php and .net to document the
api with some examples (havent tryed python to comsume the service
yet).

but everytime i try to request a tokem i get this error

HTTP/1.1 401 UNAUTHORIZED
Date: Sun, 07 Feb 2010 23:33:39 GMT
WWW-Authenticate: OAuth realm="OAuth"
Vary: Accept-Encoding
Content-Length: 27
Content-Type: text/html; charset=utf-8

Invalid request parameters.

this are the parameters i'm sending

[oauth_signature_method] => PLAINTEXT
[oauth_signature] => fceb3aedb960374e74f559caeabab356%26
[oauth_nonce] => 4b6f4dd3bd656
[oauth_timestamp] => 1265585619
[oauth_consumer_key] => 5dbf348aa966c5f7f0
[oauth_version] => 1.0

the url i using to get the token is oauth/request_token

i'm not sure what i'm doing wrong, i hat and error before about
challenge.html not being found so i created the template myself with
and error message.

if anyone can shed some light on the issue it will be very usefull.