Either you are not a gold member (if the account you posted with is the one experiencing the problem then this is not it) or you are banned from Gears matchmaking by Epic. This is their response if you glitch your rank or something like that.
I can now tell you why you are stuck on local gameplay. I glanced at your achievements for this game and it looks like you were able to unlock seriously 3.0 before you actually unlocked the level 5 achievement. Now you and I both know that's impossible.
That tell you and I both that you modded or glitched your achievements for this game. So the reason is that you got caught cheating. For future references, please don't ask a question that you already know the answer to.
No no. He definitely glitched his achievements. For example, you cannot get "I Got This!" (kill 10 people as the leader in Guardian) offline as you can only play Guardian online. I also don't believe you can get the "War Supporter" achievement offline either
(Onyx the Socialite medal - play in 30 gears events). I didn't bother going any further than that on his offline achievements...