Good afternoon and thank you for posting on the Final Fantasy XIV Technical Support Forums.

To clarify, the boot file you use is still from the Steam installation, correct? The details have not been announced whether launching it from the Steam Library will be necessary or if you can launch it from the Steam installation.

When trying to launch the game through the Steam Library, does this error message occur immediately, or does it begin to download an update and fail part way through?

Have you attempted to reinstall the game from the Steam Library?

We hope we can be of assistance in helping you enjoy the exciting world of Final Fantasy XIV!