You can't just copy a 100 install to another location. There are registry settings and defined paths.

Sorry, I wasn't clear.  I copied it over to the new server and then proceeded to attempt to run the NEW version pointing to this copy, in case it was an issue with the old location.  EITHER WAY, pointing to the old or a copy of it, I got this same error.

Can you access the Sage 100 2020 and open it?  Copy your 2021 icon it created and change the path to point to 2020 and see if you can log in

I accessed it on the original server and I accessed the copy on the new server by running pvxwin32.exe and running startup.m4t.  Runs fine.  And I checked the SY_Company file for a blank record - nope.

For Standard and Advanced, to use as a source for upgrade / migration, a folder copy is my preferred strategy (vs. migrating from the Live path). 

You're right that running a folder copy Live is not recommended, but for what  Beth is trying it is perfectly effective (normally).

Log in to old system's administrator console to check the password / see the company list from there?

Not sure what you mean there.  I am getting this error before the list of companies comes up in the migration utility, but I can't get PAST this error.

I mean log in to the Administrator Tools on the old system (where you would disable PEP) to verify the company list from there.  The migration uses the Admin login to get in, so maybe there is a problem with a system file only used for the Admin login (a wild guess).

So the issue appears to be that the old folder was missing the Uninstall Information folder.  I recreated that and it's working now.