Gearheads of War

So my Xbox 360 got RROD but that's a whole other story.

I loaded my LIVE account on my friends Xbox [his Harddrive].
I got one or two achievements and left.
A day after, I go to my friends house, and play with MY Harddrive OFFLINE.
I get ONE of the achievements that I earned online already.

Now what do I do?

[So I won't screw up progress in Gears 2 + lose or mess up the achievements]

ANOTHER QUESTION:
Went to my friends [a whole different person]
and put in my harddrive- I donwloaded the flashback map pack, played on them to confirm it works- then left.
Now, the place where I played OFFLINE- I couldn't play the flashback maps [couldn't even find them] but I could still play as Carmine, Raam, and Kim [if that even matters]
What's going on?

THANKS EVERYONE~