Comment 13 for bug 216483

@mash and @Ryan: You might want to have a look at bug #224085 (this bug here in fact may be considered a duplicate of that). Probably the things suggested there will help you as well. For me (and some others) on KDE, it helped to just add

  <!-- modification in order to KDE users can mount -->
  <policy group="plugdev">
     <allow send_interface="org.freedesktop.Hal.Device.Volume"/>
     <allow send_interface="org.freedesktop.Hal.Device.Volume.Crypto"/>
  </policy>

to the end of /etc/dbus-1/system.d/hal.conf (right before the </busconfig>). Check the output of the "id" command to make sure you are member of the "plugdev" group (Ryan is according to his initial post).