This is the first time I've run into this...my warrior has 20 energy usually. Apply Poison requires 15 from what I can tell...but I get the message of "Not Enough Engergy"? I haven't run into this before...where did I go wrong?
Quickening zephyr would make the skill cost more energy. It sounds like your in an area where something is making skills cost more energy then you have.
just an FYI, apply poison is not really that good on a warrior. I have tried running it back in the days of prophecies, and it is too much of an energy hog.
But if you really want to run it, bring a focus swap to precast it.