This matter is now resolved and was not a problem with eBox.
The problem was due to amending the hostname in /etc/hostname without making a corresponding change in /etc/hosts. Once they were both changed to match, the matter of eBox reporting an error during saving disappeared. DNS, domain and hostnames are now reported by eBox as OK.
@ Javi
Thanks for taking the time to offer assistance with this matter, especially at a time that I presume is quite busy for you. There might be an issue with resolving names but I will investigate this and open a separate thread if needed as the original purpose of this thread is now resolved.