HI once more, I reread your response, had a few more cups of coffee and found a semantic issue in our code that was causing the issue. I feel a post mortem may be in order just in case any unfortunate soul stumbles upon the same issue and starts googling.
We're using PHP and CURL to make the request. What was happening was that while we were properly encoding the parameters to generate the oauth signature and when we set the POST status using CURLOPT_POSTFIELDS, we had failed to encode the status when generating the (comma separated) http headers set using CURLOPT_HTTPHEADER. The unencoded comma in the header of course made the headers invalid. Thanks Taylor. Without your nudging me in the right direction I'd probably still be banging my head against the wall on this one. -- Twitter developer documentation and resources: http://dev.twitter.com/doc API updates via Twitter: http://twitter.com/twitterapi Issues/Enhancements Tracker: http://code.google.com/p/twitter-api/issues/list Change your membership to this group: http://groups.google.com/group/twitter-development-talk