iphone - Changing bar button appearance causes crash -

I am optimizing MFMailComposeViewController To change its UI, I have detected the UIBarButtonItem and changed it using it:

  [[UIBarButtonItem presence] setTitle: @ "" ];   
 I have been crashing in my other classes where I had used  UIBarButtonItem  with text, I decided to use those custom buttons for the bar button is. I am also using the stock kit in my app and now I am crashing in the twitter login screen when the keyboard appears with the toolbar (next / previous and in the done button).  
 
  
 Is there any way to assign a customview to the ShareKit's Twitter login screen buttons?  
 Is there a way, other times the button items in my app are crashing? If both are not for the above, then remove those buttons?   
 Thanks.  
    < P> 
 
  UIBarButtonItem  There is no method for documentation proxy in  setTitle .  
 In the document, you will find the method