Noob needs cross class ability question answered please :(

[Bixby]

Were you level sync'd by any chance? If you're sync'd by way of doing FATES or Dungeons, and are below the level you learn the ability you're trying to use (or the level where you open up that available cross class slot (you get another cross class slot every 5 levels I believe?)) you'll get that error message.

It's only the level at which you open up the cross-class slot. The level of the ability doesn't matter. Stoneskin all up in the level 10 guildhests.