Cannot install macOS update with error "cannot verify this update" While installing the macOS 10.12.6 Sierra update from the Mac App Store, my system rebooted with the error, “Cannot verify this update.”

I’m trying to upgrade from macOS 10.12.5 to 10.12.6.
Try downloading the macOS Sierra 10.12.6 Combo Update instead. Then open the dmg file and run the installer.

The combo updater includes all minor updates since the .1 release, and it is therefore larger than the delta update. However since it reapplies any system changes brought on by previous updates, it should resolve any issues that came up during regular updates.