You will likely see one of the following variations:
This error typically prevents the Minecraft Launcher from syncing with the update servers, leaving you stuck on an old version or completely locked out of the game. Minecraft Error 437 Download UPD
The simplest fix is often the most effective. Ensure that your internet connection is stable. If you are on Wi-Fi, try switching to a wired Ethernet connection for the duration of the update. Restarting your router can also clear up any temporary network glitches. Run the Launcher as Administrator You will likely see one of the following