Are you using Tableau Server 7.0.8--if not I would recommend upgrading, otherwise send the above information with the logs (http://kb.tableausoftware.com/articles/knowledgebase/creating-tableau-server-log-files) to our support team at firstname.lastname@example.org
tabcmd export works for me. I'm using Tableau Server extracts with SQL Server.
Found the reason. The reason why it didn't work for me was because I was using desktop 7.08 and the server was still 7.0, so many things didn't work including tabcmd export and also server select filter action. Tableau's backward compatibility isn't that great :S