download Apk

Hello Friends,

     I have created a game in Unity for VR which is a completely 3D game.  and Put one Button Which is to Install an Other APK file from the server. when the download is complete it will show an Android install app Panel and an app is completely install in my device also. but when i hit a open button it show like 2d panel and after 2-3 Seconds the app will be closed again i hit the open button at second time it will completely run so what is problem to open in first time please help me