http://forum.square-enix.com/ffxiv/threads/16706-For-Developers-Achievement-can-t-be-done-after-patch-adjustments
Just for the record, i write this info here too.

For further details, see my first thread.

Bug: 100000 gil reward by a single leve can't be accomplished anymore.
Reason: The highest gil basereward + all boni and multipliers sum only up to 98540 gil.

When = always (under investigation since end of march 2011, but probably the patch Nov. or Dec. 2010 disabled this achievement)

Adjustments need to be redone, to give players the chance back to get this achievement.