How to abandon Levequests

[Niwashi]

While crafting and gathering leves are specific to a particular class, the combat leves can be done by any combat class. There aren't any that are specific to Disciples of Magic.

[Enkidoh]

The only time that there is a class restriction on levequests is if you undertake one as a specific class, and you then change classes before turning it in for the reward, you can't complete it until you've switched back to the class you undertook the leve as. So it's likely you've already done that quest as a mage class but haven't yet turned it in and are trying to get the exp on another class like MRD, hence the error stating that you need to be a Discipline of Magic to do so.