My app will no longer run under Snow Leopard, runs fine under Lion.

My app will no longer run under Snow Leopard, even though it was originally written for Snow Leopard. It runs fine on my Dev machine under Lion. But when I test it on my Snow Leopard Mac Mini the app starts but the window does not appear. Going to file, new window does nothing. My depolyment target is set to 10.6. Is there something I did to make my app lose Snow Leopard compatiblty?