samba - Oct 2016 - "domain logons" meaning in context of NT_STATUS_INVALID_SID

hi everybody

I'm hoping one who has deeper working knowledge of Samba 
would not mind to explain why - when I have: domain logons = 
no | in my BDC then it fails (only that BDC, ver. 4.2.10 
classic NT setup with PDC+BDC) to authenticate, with errors 
like:

check_sam_security: make_server_info_sam() failed with 
'NT_STATUS_INVALID_SID'

SPNEGO login failed: Indicates the SID structure is not valid.
session setup failed: NT_STATUS_INVALID_SID

I'd very much appreciate if somebody could explain.
many thanks.
L.