I had the same issue.  I finally was able to fix it by going to add/remove programs and repairing the Actian PSQL v13 workgroup.  I did it on the server and then on each workstation, and since then it has been working fine.  Fingers crossed!

Thanks for the reply. I just did this on the server and 6 workstations, I will post back with results in a few days!

Unfortunately this didn't solve the issue we are experiencing.  Had to "repair" every install today to get working.

Sorry to hear that.  Mine has been working OK since i did this.  I was troubleshooting for a couple of days before this fixed it though.   The only other thing i think i did was to disable IPv6 on the server.  Some of the online posts say that sage 50 does not like IPv6.  But when i was troubleshooting it did not seem to change anything.  

I hope you are able to get it working!

I found that when a user has an issue getting sage to open, there's some bug that causes a file to get locked. I've found that closing the following files from the user session on the server; PT.lck and SUA000021.lck for the trouble user, then having the user restart their computer seems to help. But sage has never found a resolution for me, just this bandaid.

While I have been researching this issue I have noticed that if you monitor the root company directory. (I.E. sage/peachtree/company) One can see the file SUA00021.lck populate temporarily when a user initially logs into PT. It seems this file is meant to very briefly lock the directory until the user can be placed in the proper store company folder. After the user gets placed, the SUA00021.lck file is should be deleted/removed automatically from the root company directory. Afterward a .lck file should then be placed in the needed company folder the user is attempting to access locking it so no one else can access while the user is logged in. It seems the problem is the process that is supposed to remove/delete that SUA00021.lck file is not working properly. 

    I have found that closing the SUA00021.lck file, found in "open files" on the server in the "computer management" program will most of the time, allow all users to log in. On occasion the user that populated the SUA00021.lck file, found in "open files", needs to reboot their computer after the open file is closed. If that user continues to create the SUA00021.lck file, you can uninstall their Actian PSQL program and reinstall. 

    To uninstall, you can find it near the top of the program list under "uninstall or change a program" in the control panel. To re-install open the sage installer files and go to the following path:

Sage 50 2020 Disk\PervasiveMin

After doing so run SetupWorkgroup32_x86.exe 

While installing the program, make sure to install it as a service. 

    Hopefully, this helps others that are running into this issue. Please let me know if anyone knows of a permanent solution to this problem. I know that Sage is aware of this and I cannot believe this has not been fixed or addressed. This has cost our company a lot of time and money. We are extremely disappointed in sage and hope there will be a very quick resolution provided by them soon.