Although an Avast user - I would be surprised if Avast Secureline VPN supports Android 4.1.2
Or possibly the other way round, Android 4.1.2 not supporting Avast Secureline VPN, e.g. not having the the required functionality to run the Avast Secureline VPN program. Which is probably why it isn't available in the google play store for Android 4.1.2
You have posted in the Avast Mobile Security sub forum, do you have that installed with Android 4.1.2, I would have thought you may have the same issue there.