I have completed 25 challenges in halo 4 and But I have yet to receive the Achievement for it. Any solutions to the problem?
Did you completed every challenge while beeing online?
Or did you do 25 offline challenges (campaign)?
otherwise... try to do a few challanges again, to go sure you really reached 25 :)
Otherwise try the Xbox-Live Support via Twitter.
MrD33k / Darkgenesis28