Android app installation failure
If after executing of a command
adb install com.example.package.apk
you received an INSTALL_FAILED_VERSION_DOWNGRADE error but there is no com.example.package application on a device I have an idea for you.
It seems that somewhere in Android system cache still persists a record about application. But there is no such application in launcher’s app list.
Solution is the following: try implicitly call uninstall before install
adb uninstall com.example.package
It helped me and solved this strange problem.