Is there a glitch to getting 'Spartan Graduate' achievement in Halo 3?

[chu chu treyn]

I'm new to xbox live and i like getting armor in halo 3. i read you have to get 'spartan graduate' to get ODST armor, which is my fav. I got 5 EXP but no achievement or armor. I was wondering if sometimes it glitches and says you dont have the achievement, even if you do? If so, can it be fixed?

 

[Player 1]

No, just keep playing and you'll most likely get it in a game or two.