Thank you. Unfortunately, that doesn't work.

I go to the "Forum Configuration" screen and maximize the subset called "User Settings" where I find "Trust New Users" and "Lock New User Trust Setting". Both are unchecked. I have tried every combination of checked and unchecked on these two boxes.

I have tried a similar thing under "Forum Administration>Forum Users" where I attempt to change the trust status for an individual user. Here I have also checked or unchecked the "Lock Trust" box.

None of these variations allow me to uncheck the "Trusted User" box for an individual user. That box remains checked and grayed out.

Thank you for the pointer to the user manual. According to that, I should not be seeing this problem.

Thank you very much for the offer of personal tech support. Very generous.

I have solved the problem with a workaround. I changed the trust setting for new users to not trusted. Then I created a new user with a name similar to the user I want to un-trust. Then I deleted the offending user, and renamed the new, untrusted user to the deleted user's name.

I can do all this because this is a small intranet site and the user in question is a shared username with very limited permissions.

Prior to this, I attempted to address the issue by cracking open the user tables in the database and changing the trust status from "true" to "false." That was not successful.