"The quiz cannot load with your current settings. Please check your quiz question options and make sure you have a few quiz modes selected."
This error has been appearing on my kanji quiz for several days now. I have not changed its settings in months. The quiz will work normally until there is 1 kanji left "to study today." Attempting to study it generates the error message shown. When the quiz refreshes for the next day, it works normally until again arriving at 1 kanji left to study, which will generate the error yet again.
How can I figure out which kanji is causing this to happen and remove it (or clear the error in some other manner)?
This is probably caused by a discrepancy between your schedule and the reference database. In my case, I experienced this after a reading I had previously studied was removed in an update.
If you only have one item to review, you may be able to identify it by opening the schedule and clicking on the red number. Michael will probably need to fix the discrepancy for you. I don’t know of any way to do it without his involvement.
It looks like your account is still on the old, legacy setting
for "kanji reading filter" under Kanji in settings. This system is
no longer being maintained, and while I cannot say exactly what
changed to cause this to come up, I am fairly confident that it is
tied to something with this system.
Specifically, it seems in most cases, that the user (like
yourself) has it set to hide kanji rare readings. At the same
time, on most of the "ghost" kanji, it tends to be the case that a
rare reading has been marked as known, confusing the older system.
The newer system does a MUCH better job of handling cases like
this. For you (and most people), if you're willing to give the new
system a try, I'd recommend "no extra readings" as the option to
choose.