Hi Mark. Indeed, I am confused. I am not yet familiar with Hyperkiity internals and code, and I must say it is currently like fog to me. :-)
Indeed, rebuild_mailinglist_cache_for_month made me think this was a monthly job.
I had made some lists and deleted them shortly thereafter. I managed to add some lines likes raise Exception(locals()) in some of the code, which revealed that a deleted list was being referred to. I have no idea how to purge this. I looked everywhere in every table in the database to find references to the deleted table, to no avail. I deleted all the queued, jobs in Django, to no avail. I rebooted three times to no avail (highly unscientific), And now, for no obvious reason, the error has stopped appearing. it definitely did not stop after deleting Django queued jobs - although perhaps something takes time to propagate, or there is something stuck cached in RAM?
It's nice that it stopped but I feel a bit uncomfortable that creating a list and deleting it a couple of hours later can cause the log to fill up every minute with these tracebacks. The exception raised in the code simply says <MailingList matching query does not exist>. It would be great if the error could name the list. I think that would be helpful. It would make it clearer to people what is happening at least, a lot faster. Python tracebacks don't show the values of local variables, unfortunately.
Andrew