Did you use a DTP-ledboard, like a Sinkpad or Noctigon. That really helps cooling the led at higher currents.
I did a test on that led, and though the led of the test performed well, another led that I had worked less well, and some others had problems of dying leds too. Perhaps it is hit or miss with this led. The test is in this post (together with 3 otherUV-leds):