This problem came to me in Xcode 4.2 because i had added one property on button and then that property is synthesized...
As i remove that property and synthesize paraphrase. my program stopped working...
i thought that doing that silly mistakes makes me create new project again....i did this twice.
Then when i developed a calculator then i got angered and searched over net but did not got the problem solved.
Then after a long search i came to know that button's delegate were still assigned.
So i gone to "Show the connections inspector" in right corner and removed the delegate...and my program started working..!!
hope this would help you guys.....
Thank You..!!