This is a snapshot of what happens to my screen after clicking the advancement button. I had reached level 15 normally and clicked the advancement and this came up. I have tried relogging and completely restarting the client but no luck there.
Class is Wizard
Edit: The Devs have stated that this as a known issue.
3. Unable to advance in class
We are aware that some of you are experiencing problems when trying to advance in class. The dev team is currently looking into this and an announcement will be made as soon as the issue is resolved.
Hopefully it will be resolved soon.
Edit 2: From IMC
Greetings, Saviors. Many users were unable to advance their job classes because of a bug in the UI projection. This was due to a defect in the output of our UI coding. We have fixed this issue, so you should be able to proceed with your advancement now. The change will be applied once you move zones or reconnect to the game. If you face the same issue again, please report it on our forums or through support tickets. Thank you. Best regards, IMC Staff