I don't know exactly what the problem is. I have not experienced this issue (knock on wood). Here are the things I would check...

  1. Is the correct amperage coming out of the driver?
  2. Is a solder pad on one (or more) of the stars loose/corroded?
  3. Is the system shorting out with the heatsink?


All of these should be checkable with a mulit-meter... I think!

Good luck and keep us posted,
Tom