If an "immediate" shutdown occurs while trying to drive power, the most common problem in digital amplifiers is saturation of the output inductor. A frequently made mistake is to size the current rating of the inductor for rms current not peak current. When inductor saturation occurs, the di/dt (rate of change in current) becomes very high and the amplifier detects it as an over current condition and its protection system shuts down the amplifier.
A good "rule of thumb" is to design the output inductor's current rating for 2 times the peak output current specification of the amplifier.