In my iPhone app, I have a UIButton which I have created in Interface Builder. I can successfully enable and disable it like this in my code ...
sendButton.e
You can use adjustsImageWhenDisabled which is property of UIButton (@property (nonatomic) BOOL adjustsImageWhenDisabled)
adjustsImageWhenDisabled
UIButton
(@property (nonatomic) BOOL adjustsImageWhenDisabled)
Ex:
Button.adjustsImageWhenDisabled = false