GB won't recongize my USB mixer

Macbook Pro 10.7.5. Garage Band can't detect my Phonic Helix USB mixer (it used to). When I run a system report, the mixer does show up as USB device. I have reinstalled GB11, but still no luck. Several calls to Apple have not resulted in a fix. An engineer is supposed to call me on Monday. Has anyone else experienced this and fixed it?

Bronko