Propagation error when attempting to create content in custom site

(imported topic written by SystemAdmin)

One of our operators encountered an issue when attempting to create content in custom site. He is using a non master operator account. TEM version 8.1.167. The operator is trying to create a baseline in a site to which he has management rights. The following error is displayed. Propagation error. “Your credentials are not authorized to sign content for this custom site.” Does anyone know of a solution?