I've upgraded current Target for iPad and I dodn't like the result. Now, i've tried to downgrade by deleting files but it's not working. Help!

Do I need to change project settings? Does XCode keep a backup of the project? What to do... It doesn't run on iPhone anymore...

EDIT:

The console crash log on the iPhone Simulator:

2010-05-10 00:11:02.455 iDecide[9743:207] Unknown class iDecideAppDelegate in Interface Builder file.
2010-05-10 00:11:02.456 iDecide[9743:207] Unknown class iDecideViewController in Interface Builder file.
2010-05-10 00:11:02.465 iDecide[9743:207] *** Terminating app due to uncaught exception 'NSUnknownKeyException', reason: '[<UICustomObject 0x391eb80> setValue:forUndefinedKey:]: this class is not key value coding-compliant for the key viewController.'
2010-05-10 00:11:02.466 iDecide[9743:207] Stack: (
    34047067,
    2420679945,
    34206145,
    215656,
    214197,
    4551796,
    33949999,
    4546347,
    4554615,
    2715730,
    2754518,
    2743092,
    2725503,
    2752609,
    39038297,
    33831808,
    33827912,
    2719253,
    2756527
)