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Hi. I just update Android 6.0 on my Xperia M5 and my camera, gallery, contacts and so on, he incerases permission ''screen overlay'' and ''for this settings, first turn off screen overlay from Settings>Apps'' and i accessed the settings and apps, but i was sent in ''Draw over the App'' or something and i couldn't turn off the screen overlay. So i can't use all the app;icationsin detail. What can i do? Please help me quickly. Thanks. 
I am using M4 aqua
I also faced same issue after update 6.0
I have uninstalled CLEANMASTER & Phone switchoff and reset . Then Everyting started to work fine.
Pls. Try
Try disabling "File Commander", then rebooting your phone and enabling it again. It fixed the problem for me 
It is a Android 6 issue - screen overlays are now frowned upon (these have been massively abused for fraud attacks), and are blocked by permissions. That would be good, if it were not that Android 6 names the underlying App in the error box rather than the one that attempts to overlay without permissions, so that you cannot grant permissions to or delete the latter (short of trial and error).
Factory reset is the solution... I had the same problem until I did a factory reset. After that once apps popped the overlay issue I go to permissions and this time I can actually change them unlike before when I could try sliding the switch n nothing happens.
Force stop the application
restart your device
Go to settings - apps - (application) -Turn on the required permissions.