Noob question about Runes

Ok, I'm sure I'm missing something obvious here...

I'm an E/Me. I found a rune dealer, went to the Elementalist "tab", and purchased a flame rune which should add +10 to my armor. The instructions say to double click it to add it to any piece of armor.

The thing is, it won't let me apply it to my armor. Any armor. Ever.

I've found pieces of armor, and I've bought pieces of armor, and no matter what armor I try to apply it to, it won't apply.

What am I missing? Why can't I apply the rune to anything?

you can only apply an insignia to armor with an open insignia slot, ie nightfall armor. prophecies and factions armor comes with built in insignias.

Thank you - yes, I meant insignia, not rune, my bad So, insignia's are useless to me in prophecies then?

Also, it sounds like you're trying to apply them to armor drops not the armor you are wearing. You cannot do that.

unless you have the new obsidian armour then they are useless in proph yes. You can still use runes though.

Other than Obsidian Armor, if you have any armor NOT from Nightfall, the insignias won't apply because the bonuses they give are already in the armor.