GarageBand error message

Hello, I've been using GarageBand for a few days now and I already have a small problem because while playing my loops, this error message appears (it doesn't stop the playback though):

error when attempting to synchronize audio and MIDI.
Sample rate of 48000 recognized.
Check conflict between GarageBand and external device.

Does anyone know the cause of this...? I didn't feel like I changed any setting that could have caused this to appear, plus it shows up in any new project as well..

Thanks in advance

Configuration: Mac OS X / Firefox 3.6.8