Getting 2 error messages when trying to download previously purchased, or free, apps from the Mac App Store
I found there were now 2 HD's on my desktop, Macintosh HD and Macintosh HD Data. I'm not sure what this is about, so if anyone has an info - it would be appreciated.


This is expected behavior in macOS Catalina. Refer to the Apple Support document, About the read-only system volume in macOS Catalina


  macOS Catalina runs in a read-only system volume, separate from other files on your Mac. When you upgrade to Catalina, a second volume is created, and some files may move to a Relocated Items folder. 
  
  macOS Catalina runs on a dedicated, read-only system volume called Macintosh HD. This volume is completely separate from all other data to help prevent the accidental overwriting of critical operating system files. Your files and data are stored in another volume named Macintosh HD - Data. In the Finder, both volumes appear as Macintosh HD.
  
  





  I went to the Mac App Store to download previously purchased or free apps that I had, like Keynote, Pages, even Solitaire, I get these 2 different messages.


This is apparently a server side message from Apple. Try again after some time and make sure you have an active Internet connection.