Many folks like myself have restarted their XBOX 360, loaded up there Battlefield 3 game, waited untill the main screen loaded to begin player a few games off multiplayer or even perhaps a few co-op missions with there gaming buddy only to see a little pop-up window appear on the screen saying that it could not load saved file due to it being corrupted, so in a fit off rage and after kicking the poor cat you carry on pressing the "A" button then more windows pop-up saying that you hve "unlocked" different items, once again you carry on pressing the A button, then "WAMM" all your configs' have reset, every weapon has to be fixed, just the way you had it before this unfortunate mishap, well here's a fix, it's 100% fool proof, just follow these simple steps.
 Return to your dashboard then remove the game from your tray.
 Click the "XBOX" button.
 Scroll to "Settings"
 Go down to "System Settings" press "A"
 Scroll down to "Storage" press "A"
 Select "Hard Drive"
 Select "Games and Apps" press "A"
 Look for Battlefield 3 press "A" (you are now in the battlefield 3 folder)
 Scroll down until you see "PROFILE SAVE DATA" below it you will see "saved game" press "A"
 Select "Delete" then delete this corrupted file
Or if wish you can move it too, "Cloud Saved Games" that is if you are a little bit unsure about deleting this file. Another method you can consider is clearing out the "cache" which is not a bad idea to do every few weeks, it's not much different that cleaing out your web browser on you computer/laptop.
 Follow steps  to  as mention above.
 Press the "Y" button (Device Options)
 scroll down to "Clear System Cache" press "A"
When you press the "A" button a window will appear stating that "This will preform maintence on your Xbox 360 storage device. Do you want to continue?" if you do select "Yes" this clearing the cache take about 30 seconds, it's totally safe to do so.
You will not lose any data for your multiplayer games or any co-op mission that you have done in the past, the simple reason is that ALL off your data is stored on the DICE/EA servers' thus you do not lose anything, all your weapons/loadouts/kits/ribbons/medals (well you get my drift) etc. As for all your achievements, they are stored on your xbox, deep inside the system, plus they are stored on the xbox server, just check out your xbox live online account (via web)
Now, you have followed these steps to the letter, it's time to put your BF3 game back into your xbox as you normally do, but first, turn off (power down) your Xbox, restart it up, and you will find that this annoying "corrupted data" has gone, your ribbons/medals/kits etc are still there, but you might have to re-fix your weapons to the way you want them, then your good to go once again...
[Tip] Let the game save all the data before you go online, wait till you have re-fixed weapons and have seen "saving" before you start fragging folks, this is writing a NEW saved file to your game.