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
Another option is to change the text color (to light gray for example) for the disabled state.
In the storyboard editor, choose Disabled from the State Config popup button. Use the Text Color popup button to change the text color.
Disabled
State Config
Text Color
In code, use the -setTitleColor:forState: message.
-setTitleColor:forState: