That move is too advanced for you.

[Ekcin 2,404]

I get this message when fighting champion creatures (except a few like spiders and wolves) when attempting to take a stance. That is even the case when a chance for taking a chance is displayed.

 

What does determine when the move will be allowed, CR, weapon skill, FS, fighting subskill, mix of all, or characteristics?

[Yldrania 1,425]

AFAIK it's the weapon skill only that determines. Primary weapon, if I'm correct.