iOS crash problem: Received memory warning . How to solve that?

Hello guys,

I am developing a card game. I received the following warning from Xcode:

Received memory warning... WARNING -> applicationDidReceiveMemoryWarning()

When the game changes scene from Main Menu to the Game Level, it crashes. It doesn't happen in all phones of the same model though ( tried with different iPhone 5 devices, I get the message in some of them).

What might be the problem? How can I solve it?

Thank you