Hello Martha
How are you testing the app? It seems the emulator does not support screen transition. If you are creating a debug APK file and testing on a device, it might be that the device does not support transitions or an option has been set (power saving/memory saving?) which has a negative effect on, erm, special effects.
...or it might be your code. If you have selected Screen Animation in the Screen Attributes Tab, then there is no need to also set it in the code. It's probably a good idea to stick with one animation type for every screen transition too - you don't want to give your app Users a headache :)
So, easy test - try the attached project file (.aia). Working perfectly on my devices.