Maple Warrior 30 book glitch?

[Reddish]

So today I decided to buy a MW30 book and try my luck:

In the picture above, you can see my MW is currently at level 20, with +1 level from the Leafre card set. But when I double clicked my MW 30 book, I got an error notice saying "You cannot use Mastery Book":

I've tried relogging, changing locations, changing the Crusader Codex card set so I don't have +1 skill levels, but the end result is I still can't use the MW30 book.
So, what I'd like to know is if there is a glitch with MW30 books with Mihiles (and other classes), or is it just me?

[ultimax21]

How about try adding the last sp so its lvl 20 instead of 19? Although normally you shouldn't need to do this anyways...

[Dark Link]

How about try adding the last sp so its lvl 20 instead of 19? Although normally you shouldn't need to do this anyways...

It's already level 20? The "Skill up" button is greyed out.

[Reddish]

It already is level 20.

EDIT: Darn I type slow

[Kaasoljoyyx]

Most likely reason is because you're a mihile. Just notify it to nexon and they'll add it to their bug list.

[Marksman Bryan]

Didn't Jett's have the same problem?