Unable to get synthesizer working

Hello

I've been playing around with MuseScore a fair bit today, and I am unable to get the synthesizer working in anything newer than the 0.9.4 package that comes with Ubuntu. I have compiled the trunk from the Subversion repository but when I run it I get the following errors:

stuart@cassini:~/svn/mscore/trunk$ /usr/local/bin/mscore
JackAudio() midi 1 audio 1
JackAudio()::init()
unknown option character l
unknown option character l
unknown option character l
unknown option character l
unknown option character l
JackAudio()::init(): failed
no JACK server found
~JackAudio()
init audio driver failed
sequencer init failed
write session file
auto save
write session file

Jack is running (the latest from Subversion too) before I start MuseScore, and other applications are working it including QSynth and my MIDI keyboard. A Google search for "unknown option character l" hasn't helped me much. Any ideas?

Stuart