A week or so ago, I was getting crazy bombarded with Trackback spam, and when I would de-spam with Blacklist, I would get an error message that I didn’t understand, and so I assumed the de-spam wasn’t taking. So I went into IP banning and pasted the IP address from which the spam came.
The spam stopped.
Nothing I tried to fix the comments was working, so I went in and deleted the banned IP address. Now comments work again.