Thanks for sharing the update, ballade4.

The Windows user permissions may be the reason why you're getting this error, and not the users added in QuickBooks Desktop. It can also relate to the Bank Feeds process since you're using the server. 

To prevent the issue from happening again, I'd recommend contacting the hosting provider or your IT professional to review the permissions.There might be a different user with full control that modified your access rights.

You might also find this article helpful regarding the QuickBooks users: QuickBooks Desktop Users and Restrictions.

You're always welcome to leave a reply here if there's anything else you need. I'm just a post away to answer your questions.