[Hall of Famer]

The error 'Something is very, very wrong' is generated when the database structure of table prefix.users does not match with the mysql insert query in register.php. I am sure your table prefix.users structure is completely different from Mys v1.2.3's. This may be the cause of your problem. Also its a bad practice to replace all your old files with new script files without looking at your database structure. You may be experiencing similar problems with creating and adopting pets too since I do not believe the database structures are compatible.

Anyway in order to upgrade from Rusnak Script, you will need to first upgrade to Mys v1.1.0, and subsequently v1.1.1, v1.1.2, v1.1.3, v1.1.4. It will then be possible to upgrade to Mys v1.2.2 using the megaupgrader, and a final upgrader from Mys v1.2.2 to Mys v1.2.3 is the last thing to use. This is under the assumption that you have not installed any old RA mods/addons. If you have installed any old Mods/Addons, the game is over and you will have to start over. I am sorry about that, there is nothing I can do about it. The old Mods/Addons do not use the plugin system, which causes lots of compatibility issue with new releases.