I think the same thing happened to me.
After my first multiplayer game, some weapons have been unlocked (golden or not) but my credits are always at zero !
I haven't seen if I earned a lot of negative credits in this first game (like - 290 000) but I suppose it.
So now, I don't know what to do ?! Must I win 290000 plus 100000 to have the right to buy all the weapons ? Or it's not obtainable ?