Hi,
I'm experiencing a similar problem as the OP:
I'm running a custom 6.x android ROM on my Huawei P8 lite ALE-L21 and have been using Avast Mobile Security so far. However, I want to switch to Kaspersky but AMS won't let me uninstall it. Whenever I check settings->security, AMS is listed as an administrator, but unchecking the box next to it leads to an error message "settings has been stopped", returning me to the main security settings screen.
Since this seems to be the last hurdle, I hope someone can give me a hint. The Avast FAQ section and the other information on the Internet which I dug up so far were not helpful.
Bazinga uninstaller didn't work, either.
I'm grateful for any helpful reply!
Cheers,
Pat