ROG and NIN was a new class/Job added in a patch - meaning SE has to add these classes in manually into the forum class list (which they have not as yet) .

SE are aware of the problem though (numerous players have informed them about the problem already) and they have stated that it will be addressed (when though is anyone's guess). All you can do at the moment sadly is to use an alternative high level class for the forum to have the least amount of posting restrictions.