WotLK Bugged Achievement

[tyroflas]

Greetings,

I am having problem with the following achievement: I'll Take You All On (10 player)

I am casting spells,meele,wand the Rune Giant, and for months now, i am just not getting rewarded for the Ancient Rune Giant criteria, i have participate on countless of Ulduar 10 Runs, that rest of the players got credit for the achievement literally next to me.

Am i doing something wrong?