System download macOS10.12.1

The Age of this computer will Govern what newer version of macOS it will Qualify to install. Use About this Mac from the Apple Icon on Desktop - the required Information will be there.

With the above information in-hand - follow this How to get old versions of macOS and verify what version this computer Qualifies to install. Make sure to use Only Safari to commence the download as Others may not work

This will download the latest version of the chosen macOS. Example Sierra will be Sierra 10.12.6

Make a Time Machine Backup Before attempting. Notation - Mojave is the Last version to support 32 bit applications / extensions and Drivers. Catalina and Big Sur Only support 64 bit and there is no workaround.

Are there any AntiVirus, Disk Cleaner, Optimizers, Un-installers, etc installed which should be removed as per Developers Instructions. They are useless, unneeded, cause havoc and interfere with the normal operation of the OS and may even Corrupt the OS requiring a Reinstallation

According to your signature, you are running 10.10. That is two full upgrades behind 10.12.

10.12.1 is an update only to 10.12.0 upgrade.

To find out if you can install 10.12 upgrade, see this article.

What error message?

Why do you want OS 10.12.1?

The Error Message is probably because you are attempting to download an update to Sierra. This update is NOT a FULL INSTALLER of Sierra.