Yes: a moderator's rejection removes an artifact marked as "private" from the repository, so that continuing to refer to it gives this error. [See the docs](https://fossil-scm.org/fossil/doc/trunk/www/forum.wiki#moderation) for more info on how Fossil forum moderation works. Most of the info on that page is meant to help the repo admin to work out what happened, but here it's quite clear without the detail.