Augmented Reality for UE4

hi , i tried to get the mobile phone screen resolution a bit better, i tried 720,480. But the screen turns purple. Is that something familiar to you? i changed it the way you showed here (android)
http://www.unreal4ar.com/mobile-video-resolutions/

And another question, i have great porblems to get this on my phone. Sometimes the export goes well 10 times, but then suddenly it goes wrong. The export is a succes, but the app wont start. And once this happends, there is no way to get this starting again on my phone. (uninstall-install. phone on, phone off,… etc) Sometimes resetten the whole phone can help it.

best regards robert