Impossible to do my missions

Please, since yesterdey, every mission I take, i can't do it... if i need to kill mobs, when I kill them, they don't count.
I have already tried to quit the mission and then, get it again, but anyway...
I also have changed the map, and get other missions, but even so, it is still not working :(

can anybody help me?

Make sure you are not in a raid group.

ohhh, it is right (:
sry about that, but its my first time playing wow.

thanks a lot!