After several hours of downloading Monterey the Software Update panel indicated an error. It seemed the error was with the Install phase, not the download phase. In an effort to help things along I rebooted. My only option was to download it all again. Back to 9 hours remaining.
FML…
Sorry about that, for sure not so pleasant experience.
hopefully it goes well now, is this with a M1 or intel CPU? Maybe nuke it this time and do a clean install? not sure, but maybe the error has some files around and may have some issues after …
Believe it or not, same thing happened to me with my refurb M1 that I just got today. This is a bad day for upgrades, apparently. 
Finally installing… (20 characters)