As Tonie wrote here http://forum.joomla.org/index.php/topic,119467.0.html
the ability for logged in users in Forge for the Joomla! project has been disabled after a request from the Q&T director. The devs are setting a freeze on new artifact until after 1.0.12 has been released. After this, the ability to create artifacts will be opened again. Thanks for understanding.