Have you tried installing an application and you observe that install button cant press but the cancel button works. Its obvious something is wrong and rebooting your android device for 20times won’t resolve the issue, so here is what to do.
Either you are using screen filtering apps just like Twilight, f.lux, CF.lumen and bluelight filter.Do this to get this done:
Try deactivating/uninstall/for-stopping the screen filtering app and it will you should be able to use the install option button as normal.
Wow.. Thanks guys, had to flash my device and it worked, later installed that same eye filter and it started again. Thanks for this info, you just saved me from flashing my device again.