Originally Posted by some dude on GameFAQs
Alright here we go, this came with a little help from mello456. I took his method and expanded on it to discover the trick to get your acheivements if you used codes on accident or purpose. The problem is that once you use codes, ur profile is ruined for this marvel game and you can't unlock the acheivents. Even if you erase the game from your profile and HD it won't fix the problem but i solved it. So here we go:
1. You need 2 controllers (2 players is optional, you can do it alone but you still need 2 controllers)
2. Create a new profile on your HD and starte Ultimate Alliance. Begin story mode and just do it on easy because you won't be beating the game just getting through 1 level.
3. When the game starts check to see if the codes you used are not on therefore if you unlocked all costumes make sure on this new profile they are not selectable. if ur good to go push start on the second controller and select co-op mode. The 2nd player should now have control of spiderman. Press the guide button on the 2nd controller and load your old profile (the one you can't get achevments on).
4. IMPORTANT STEP: Push start on 1st controller and quit game. Start a new game on easy again and when the level starts push start again on controller 2. But this time if you press the guide button ur old profile should still be logged in. Same for the new one on the 1st controller.
5. What you do now is simple. You have 2 routes you can go to fix ur profile
A. You can controll both controllers or have a friend controll one. When you decide what you are doing, go for an easy acheivment with your messed up profile like 10 kills or use a finishing move 5 times. when the acheivment is unlocked check to see if you got it on ur old profile. if so, congrats, just press start go to players and turn off player 2. Then just controll player 1 and get to a save point and save on the new profile you made. Now when you play the game on ur old profile the cheats should be off and you can unlock acheivments as long as you play through the game without codes.
B. This route is for if you used codes after playing for a bit. If so, do all the steps above except for sterp 5A. Instead go ahead and turn off player 2, when i say turn off i mean under the start menu. Don't turn off the controller. (if you have a friend playing with you no need to turn him off) now you just have to play through the game and get to the point where you used the codes. Once there beat the next boss you have and make sure both players are on. Both profiels should get the achievment. After you get it, turn off player 2. save with player 1 on your new profile. Then when you quit to dashboard, load the old profile you had and when you start the game it should be fresh, no more unlocked costumes/characters and you can start getting achievments like you just opened and popped the game in for the first time.
Any questions just post here and i will do my best.
And once again thanks to mello456 for the initial solving of the problem. We make a great team huh?