A fatal DirectX error has occurred received when starting the game

[EssinayaDeBorel]

go to C:\Users\"USERNAME"\Documents\My Games\FINAL FANTASY XIV - A Realm Reborn (this is location for standalone version, don't know about Steam version .cfg file location)
and open with notepad file FFXIV.cfg
then change value in row 24 "ScreenMode" from 1 to 2
save changes & launch the game

Thank you so much for sharing this fix. It also worked for me! It also worked the weird straight line I see whenever I play.