It appears that something has disrupted nmb daemon from starting, unfortunately the information in the dialog only tells us that it’s not working, not why.
Assuming you have SSH access configured, or the system shell turned on (System -> Services -> Shell in a box), could you please provide the output for the following commands?
systemctl status nmb.service
journalctl -u nmb,service
systemctl status smb.service
journalctl -u smb.service