Following the announcement last month that Square Enix would begin allowing Steam account linking for Final Fantasy XIV players, patch 6.08 started availability of Steam linking today. While many seem to be playing successfully, Square Enix has also responded to reports that the Steam version is causing errors.
There is a response to the community reports that there are some players who get an error message when they try to launch the Steam version, which leads to the game being unplayable. They acknowledge that they're currently investigating, but because many players are still able to launch the game and play through Steam, pinpointing the issue was initially difficult.
They are continuing to investigate the issue, but released a followup statement with additional information on their findings. Square Enix confirmed that the issue can be avoided if you set your Steam profile name to alphabetical characters only. Special characters or even numbers may be contributing, so for now they advise that you be sure to set your Steam profile name to simply letters and then try to launch the game as a temporary workaround. They’ll continue working with the Steam
If you take advantage of Steam linking and you want to play the game, it won't be possible to launch it from anything else but Steam going forward, so be sure you’re all set before you link.
It does seem like they’re getting a better idea of what is behind the current error and will continue to update the community regarding Steam launch issues. With a global community that is probably using lots of different characters in their profile names, it makes sense that they will continue to work on a fix to directly address the problem.
For more on the Steam account linking process, as well as to keep up on the current launcher issue and potential resolution, head over to Final Fantasy XIV.