Android 6.0 and 6.1 Marshmallow has an annoying “Screen overlay detected” error. It doesn't allow apps to launch or having the permission settings changed.
Especially if the app needs to request a new permission android will not allow permissions to be changed when an overlay is running, thus resulting in the “Screen overlay detected” message.
This is caused by apps which are using floating action buttons or other screen overlays (elements which can be displayed over other apps).
In most cases these are apps which run in background, monitor system resources (e.g. processor, memory, battery, ...), react on events (e.g. incoming messages, ...) and display status messages, or app which extend the user interface of android devices.
It is important to note that this error is not caused by the app for which you want to change the permission(s) but by an other app and there is no way for a developer to protect his own app against this error.
Unfortunately, for Android 6 Marshmallow there is no easy way to find out the app which is causing the error. We have collected some tips and a list of known apps which may help you to get rid of this annoying message.
If you know which app is causing the error you need to disable the screen overlay for this specific app.
You will see a list of all apps that have the permission to use screen layout.
Disable the permission for that specific app. And there are more apps using a display overlay.
Disable the permission for a specific system app if one of this apps is causing the message.
If you don't know which app is causing the error there are basically two ways how to solve the error.
As soon as you have found the app and the error has disappeared, you may want to reactivate display overlay for the other apps again step by step, or just leave it disabled.
Nevertheless, the above mentioned step(s) do not help in all cases. To identify an app which is using display overlays you may ask yourself
Here is a list of apps and settings which are reported to cause this error.
And there are some custom specific UI's from different vendors like Samsung, HTC, LG, Motorola
This list is not a complete list of all possible apps.
If you know any other app(s), please send me an email to extend this list and help other users.
Here you can find even more tips to solve the issue.
How to fix the “Screen overlay detected” Error on Android - by How-to Geek
How to fix “Screen overlay detected” Error - by AndroidPIT
Screen Overlay Detected Error : How to Fix it Easily? - by gadgetraid