After updating my nexus 4 to new android 5 (lollipop) when i open an apk file, the install button not working!! Also i checked unknown source in my device settings.
What the problem? please help :(
I have used lux lite application, this application set display brighness for reading in night mode. my problem solved when i unistall this app.
This happens when you have apps that interfere with the installation.
Example: I used to have Avast on my phone. Every now and then I couldn't install an app for the problem you're describing.
I uninstalled Avast (but just disabling it would be fine) and everything went fine.
So this is it: look at the apps already installed in your phone. Chances are there is something that blocks the installation...