Using USB preamp with Garageband

Garageband will not recognize my microphone for some reason. I am using an M-Audio USB Preamp, with a Behringer condensor microphone. I have changed the input/output settings in both the mac settings and the garageband settings to "M-Audio Mobilepre USB." Garageband must recognize the preamp because it has it as an option in the input and output. The computer hears the microphone, because the input level bar in system preferences responds to sound. Garageband works fine with the built in mic, and the microphone volume is maxed, so I know that isn't it. Any help?