+1  A: 

I dont know what the problem was but after restarting the XCode, everything works fine.

tak
Now I possibly know, that I was not saving the interface builder document explicitly. I was having a wrong idea that running the app in iphone simulator will popup the save dialog, which will inturn also save the changes in the interface builder document. And unfortunatly this was not the case. So by closing the xcode and the interface builder i got the message to save the changes which i did and that led to the resolution of the problem.
tak