Using WP 3.0.1 and WP to Twitter 2.2.3 on a CentOS server, which I don't manage at all. I've got the error "OAuth Authentication Failed. Check your credentials and verify that Twitter is running.".
I've also checked all the data from the application, including erasing the older and creating a new one, but this issue remains. Twitter is active and working at this very moment I'm writing this message.