iPad app - +[CATransaction synchronize] called within transaction halting the application

Many a times when I run my iPad app from XCode to Simulator, i开发者_如何学Ct gets frozen after starting. Every time when this happens I see the below line on the console The only way to go ahead after this is to stop the XCode app, remove it from Simulator and install it again. If I don't remove it from simulator and just restarts it from XCode it again gets frozen. Any idea what that happens and what the below line indicates?

+[CATransaction synchronize] called within transaction

I would like to know if this is happening due to any glitch with the design? I have created custom tab bar in my iPad app and firing viewWillAppear, viewWillDisappear, viewDidAppear and viewDidDisappear methods myself from the root view controller.