Make sure that the client you downloaded was 1.12.1. People have been known to download others.
If you are on Windows, make sure that the World of Warcraft folder is not in Programs, the desktop is fine.
If you are on a Mac, make sure that the World of Warcraft folder and its contents are not write protected (Getinfo)
Open the World of Warcraft folder - delete the WDB folder, it is cache and will rebuilt.
Open the file realmlist.wtf with a text editor (NotePad/TextEdit)
Make sure that the realmlist.wtf's CONTENTS are ONLY
set realmlist logon.elysium-project.org
There is a folder called WFT, open that, delete the file called Config.wtf if it is present.
Start WoW.exe (Windows) or WoW Classic (mac)
I have done all the above......
I start wow.exe and I get the same message about what i stated in my first post.