Running Debian Testing, updating almost daily.
I recently started having problems with my trusty Galleon 2.5.1 installation and finally decided to upgrade to 2.5.5. Wiped out installation to start from scratch.
gui.sh was having problems connecting.
After some debugging, I added -Djava.net.preferIPv4Stack=true to gui.sh, and now the GUI can talk to the local server.