internal fault over-current protection (low load or a short) gain set all the way up over-driving the input stage of the amp and causing the amp to enter protection.
those are a few possible causes.
Kenwood amps aren't really what I'd call terrific quality. internal faults are fairly common with their amps, much like Sony's. Hopefully yours is just a matter of a short or the gain setting.
NO THATS NOT TRUE THERE JUST REALLY FINICKY WHEN THEIR HOOKED UP WRONG . ESPECIALLY PRONE TO SHUTDOWN UNDER LOW CURRENT . LONG LIVE THE EXCELON GOURIKI 1500}
I can tell you why it blew without even seeing it. one of two reasons: inadequate electrical system caused the amplifier to clip, which cooked the sub. or gain on the amp was turned too far up, which caused the amp to clip, which cooked the coils on the sub.
oops, missed one remote possibility: used a ported box and no infrasonic filter, and the sub unloaded and failed mechanically due to unloading and over-excursion.