Can't use rune!

Why can't I put a minor monk rune on my armor?
I am E/Mo. (i have 15k armor and infused and dyed)

But surley I must be able to put a vigor in it, right?

Elementalist Armor can only have Elementalist Runes in it. Same for all the armors (with Vigor of course being the exception... it can go in all armors).

vigor yes, its a general rune
but you can only use runes of your primary profession

thanks!