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Being unable to log into only one character can sometimes be attributed to a corrupt file in the locally saved settings. Find the settings files in the 'My Documents' folder (My Documents > My Games > Final Fantasy XIV) and delete that folder. Try to log into that character after that.

If this does not work, try doing a clean boot. Simply open the task manager and select the 'Start up' Tab. Disable everything here and restart the PC. This will make sure that no background processes are interfering with the game.

If you are still having problems after that, can you submit a Final Fantasy XIV system report? Simply go to the 'Config' option on the Final Fantasy XIV launcher and to the right of 'System Information' click on 'Display.'

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