For me, it was definitely the co-op that screwed me up. I had given up on this game but I tried it again tonight via co-op again. I tried to sign in my wife's account, but the game wanted to start me from scratch. So I started my single player game instead, and tried to have her account drop in, and the game gave me a message telling me to sign out first, then drop in, which I did. We played together starting in section 4-2 and I was able to get the mine mine mine achievement, and then later the upgrade achievement and the achievement for finishing the game. Something about having the co-op person dropping in to the middle of my game caused me to not be able to get any achievements without a co-op person, it seems.