Having the same problem. I applied the latest update and then was able to apply updates to all workstations that already had 2021 installed. However I was not able to perform a fresh install of 2021 on a new workstation.

so we had a very similar problem.  Updated server just fine.  Then when opening SAGE on workstation it just threw up a message that "update has been run on server, you must first update workstation.  SAGE will now close".  (or something similar to this).  I also tried uninstalling/reinstalling, to no avail.  I could not get ANY support.  After 2-3 hours I stumbled upon a file under the SAGE\PEACHTREE\COMPANY\UPDATES folder called PTXA2021.1.1.  Ran it on each workstation and it worked.  But since then, I have been trying to get support to explain to me why/how this happened and how to avoid it next time.  But have been unsuccessful.

For clarification: That's the process I followed for each of my workstations as well. I never really used the in app update method because I always found it easier for the workstations to run the updater directly from the updates folder. That process worked for all of my existing workstations. A new workstation that had not yet had 2021 installed is the one acting up and that seems to be similar to OP's post where they uninstalled Sage 2021 from the workstation and now are unable to install it now that the server has been updated.

*edit - thought you were replying to me, sry!

We suggest browsing to the server from the workstation. Look for the Peachtree installer file.  Run the original program and subsequent updates.  

Make sure you turn off your antivirus but leave the firewall on.  

As I stated in my original post, I have followed exactly that procedure. We are on the workstation, browse to the server, find the install file, and start the installation. The problem is that it won't complete the workstation installation. When it gets to where you have to tell it where the company files are located, no matter how we have the drive mapped, it tells me " there is not a valid sage 50 centralized data location on the location of the mapped drive". The installation will not complete. Other suggestions?

You can install the workstation with a local program path and data path, and then edit the Peachtree INI file and change the data path to your network path, after the installation. However, before changing the INI file to the network data path, make sure that you open Sage 50 locally and activate the software. If you should need any assistance with this process, please don't hesitate to reach out to us.

I'm going to try this today. I'll respond to let everyone know if this worked. This program has almost become way more trouble than it's worth. Maybe it's time for a new accounting program.

Sage 50 2021 is a different animal from the prior versions - updated version of Pervasive, UNC data path suggested vs mapped drive, etc. I hope your frustration ends with this, but please know that we are here to help.

Sorry but that doesn't make me feel any better. I've been with Peachtree since it was a DOS program in the 1980s, through the transition to Sage, but it just keeps getting harder to manage every time they do an update. I want a program that WORKS and I can manage on my own, without having to call in professionals when it doesn't work the way it should. There is NO reason why upgrading should be this hard!

This did not work for us. The PTXA file stopped and said it couldn't run unless a version of Sage is installed on the workstation, which of course it is not, because we can't get it to install. We even tried installing the Sage 2020 on this workstation, hoping it would let us open it just long enough to exit again, so that the upgrade file would run. No luck. Even the 2020 stops when we get to the mapped drive (the same one we were using before this whole upgrade mess) and gives me the same message about there not being a centralized data file at this location. So, there is something completely messed up with the server upgrade that it didn't mark a "centralized data location" so that new workstations can find it. My next move may be to try to reinstall the 2020 version on the server to see if the workstation can then find it to install on the workstation. I wish I could bill Sage for all the time we've spent in our office trying to make their product work. I'm about over this completely.