Have they been updated to the latest database version?  Have you tried clicking "refresh companies" on the login screen?

Are the archive company databases updated to latest version?

Have you tried clicking "Refresh company list" from the company login screen?

I have this problem often. The best way to fix that is to restart 'SQL Server (SAGE100CON)' service on the server.

You will need to locate the file services.msc. Mine is located at C:\Windows\System32. Open that file and locate the service SQL Server (SAGE100CON). Right click and select restart.

Once you restart you should be able to refresh the company list and see your archives.

I hope this helps!