The unit comes with a 9v battery inside for use on systems without phantom power. If you are using phantom power to operate this device, a dead 9v battery (due to natural draining over 6-12 months) will cause phantom power not to go through the unit. The solution is to simply remove and not replace the 9v battery. Then phantom power will power the unit correctly.

So basically having a dead 9v battery even in a phantom-powered hookup will cause the unit to not function. Removing the 9v battery and not replacing it will correct the functionality.