"The Installer information on the recovery server is damaged" when installing macOS Sierra
You need to restart the Mac and keep holding ⌘+R, and you will get the Internet Recovery screen. Connect to WiFi or via Ethernet and you will be to reinstall the OS.
A couple things to watch on machines that have been off for a while:

check the date and time, if they are not within 4 minutes of reality, the check for valid software can fail.
Be very clear if your macOS installer was downloaded a while back, the signing certifications can be expired.
Be aware that even an unexpired certificate can fail to install if there are errors in the network or disk.