On the front admin page of the marks return system, the class code I am marks returner for is missing from the list given on the drop-down menu.
I am marks returner for a certain class code. That code is not included in the list of classes given on the marks return system.
The cause is that you not the electronic marks returner for that class code. You may be marks returner for others, the class codes of which are shown.
Electronic marks returner is a Pegasus role which the class manager can assign. Many users are themselves the class manager for the class(es) they are marks returner for, can do this for themselves in Pegasus.
If it is a University-wide class code (e.g. EX codes), the marks returner role can be assigned by Student Business.