I have met the same problem, here is the header:
OAuth oauth_nonce=“glxomnct08x0gfialw”, oauth_callback=“http%3A%2F%2Fwww.baidu.com”, oauth_signature_method=“HMAC-SHA1”, oauth_timestamp=“1373014401”, oauth_consumer_key=“9BFD1XOiVFHrnS7Hw78yA”, oauth_signature=“Qm2WJtOMYAJ8FpOfBAar5THKbdo%3D”, oauth_version=“1.0”
nearly the same as the sample in https://dev.twitter.com/docs/api/1/post/oauth/request_token
OAuth oauth_nonce=“K7ny27JTpKVsTgdyLdDfmQQWVLERj2zAK5BslRsqyw”, oauth_callback=“http%3A%2F%2Fmyapp.com%3A3005%2Ftwitter%2Fprocess_callback”, oauth_signature_method=“HMAC-SHA1”, oauth_timestamp=“1300228849”, oauth_consumer_key=“OqEqJeafRSF11jBMStrZz”, oauth_signature=“Pc%2BMLdv028fxCErFyi8KXFM%2BddU%3D”, oauth_version=“1.0”
Do you have any idea of it? BTW, how to post a new topic on Discussions?