CoreAudio : Selected driver not found

I am trying to record a test under GarageBand using a Samson C01U microphone and I get the following error while launching the application (or switching the input to my microphone) :

CoreAudio : Selected driver not found (-10202)

I am trying to achieve this under Mac OS X 10.4.11 Server, which I understand is unusual but should be doable. My Samson Softpre applet doesn't work under Leopard and it dramatically improves the recording, so I need to go back to 10.4 somehow...