I installed version 6.2 and configured mAirlist. My database was configured with PostgrSQL14. Everything was working fine.
Now I installed 6.3.14 (Advanced Server) , and followed the instructions on this page :
https://wiki.mairlist.com/tutorials:general:getting-started:v6_3:v6_3_updating
I start the configuration program and got the following error message : 1 error(s) occured during initialization.
and a few moments later the error message :
Error creating object mAirListDBPro: Unknown class: mAirListDBPro
What can i do to solve this ? 
/edit
I wanted to use a SQL database because i thought mAirlist will run smoother with an SQL database instead of 1 single database file. (Previously i used Sam Broadcaster who used also an SQL database for this reason).
Anyway … As i see now, my version does not support an SQL database, is it possible to convert the SQL database to a “normal” mAirlist database ?
What edition of mAirlist did you use on the 6.2? I’m wondering why that supported SQL and now it is no longer supported. Was that a demo Version or also a fully licensed one?
Nevertheless on mAirlist 6.2 you should be able to open the databse and do an export/ conversion.
After that add the database in your 6.3 version.
I heard about the database trouble on SAM, but I can assure you that even the local mAirlist Database is much more robust. At least I have never faced any problems.
On my 24/7 server I run the largest edition in combination with a PostgreSQL Database, it gives quite good performance boost on scheduling. Other than that I don’t see any difference to my local DB on my Home-Studio.