Discharge of Misery Not working?

Alright doing a Cast on Crit Discharge of Misery as an assassin.
But no matter what skill I use, it just won't trigger. The skill tooltip tells me that the attack will trigger a spell, but no discharge whatsoever.
Triede with Cyclone (but guess that is channeling), with dual strike, flicker strike, all the strikes. Nothing seems to work.

Anyone got any brilliant ideas or something I overlooked?
Help much appreciated.