You have set the cancel button and other button's titles to nil. You should set some title for the cancel button:
UIAlertView *jailbreakDetection = [[UIAlertView alloc]
initWithTitle:@"Jailbreak Detected"
message:@"This application will not run while a jailbreak is installed."
delegate:nil
cancelButtonTitle:@"Close"
otherButtonTitles:nil];