First of all, I know its wrong posting a bug here, but on the EU forums, there is no bug report it seems, now to the issue:
Tricks of the Trade does not apply at all, nowhere it seems. There was no annoyance buff, and we were hoping to have an easier Skittish run than what we ended up with. When targeting with Macros or the spellbook itself, it just return the error: Invalid Target. So yeah, what on earth is going on?
The forums are not the place to report suspected bugs, as the developers do not read the forums.
The correct way to report a suspected bug, is via the in-game bug reporting tool.
While in game click on the Red question mark (?), and select HELP.
From the left sidebar in the window that appears click on “Submit a Bug”, and then follow the destructions.
I assume that you have the more obvious requirements checked out. Like being in the same party/raid with the player you wish to apply tricks of trade to. Also that the player is not using any mount at that moment.
What is less obvious is the buff that you may get in a few ways, giving you or the target full immunity to this skill. It is enough that one of you has the buff, as skill applies to threat transfer between those characters.
One would be the Neural Silencer consumable:
More likely however it would be Neural Autonomy card.
This card can be slotted into the trinket from Mechagon area:
If that is not the case and interface reset doesn’t solve it, do send a bug report indeed.
Probably the blue punchcard on the tank or your macro is broken.