Can't set anti-theft as device administrator

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Hi all,

I have a Samsung galaxy S4 GT-i9515 upgraded to Lollipop 5.0.1 , the phone is rooted.
The problem is that I just cant set Avast anti-theft as device administrator , and it keeps signaling that in the problems section.

When I manually enter the "device administrator" section I can choose among S voice, Android device administrator and the name I gave to anti-theft, "iphone" in this case.
when I tap on iphone it opens the permissions page and then activate.
But no way to get the "iphone" checkbox flagged .



Any hint?
Did I go wrong somewhere?

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seems i cant submit a print screen to this topic.
Is there some way to upload a photo to here?
Thanks!

[Eddy]

Manual:
http://files.avast.com/files/documentation/mobile-security-user-guide-en-v2-4-updated.pdf

Tutorial:
http://www.techrepublic.com/blog/smartphones/set-up-avast-anti-theft-on-an-android-phone/

You can use "Attachements and other options" if you want to show a image.