This is caused by the security enhancement function applied from the Marshmallow OS or later. This message appears when you’re running a floating app, and then start a newly installed one, which requests access rights. Floating apps include the chat heads of Facebook Messenger that can appear floating above other apps.
How to fix it
1. Go to follow these steps.
For non-Samsung smartphone users:
- Open the Settings
- Tap the magnifying glass at the top right
- Enter the search term “draw”
- Tap Draw over other apps
- Alternative route: Apps> [Gear icon]> Draw over other apps
For Samsung users:
- Open the Settings
- Then Applications > Application manager
- Press on More > Apps that can appear on top
2. Find you what apps have permission to draw over the screen.
From here, you'll need to track down the app that needs permission to use a screen overlay — usually the app you were using. Toggle off apps one by one as you go back to the app you're trying to use, and you'll eventually find the culprit. When you've found it, tap the toggle next to it to turn it off, and you should be good to go.
Unfortunately, due to the security concerns highlighted, there's no full-on "fix" for the issue of screen overlays blocking the use of other apps.