dear jb_bsd,

Many thanks for your kind attention.
Actually, the group creation was needed by an application other than apache but that's minor.

First step from your instruction was done some time ago following the tip from Sergiu-IT (earlier in this here thread: "Try to manualy edit the /etc/group file.")

However, the idea of checking the group (second step from your instruction) is wholly your merit.
I did as you told and the box replied "/etc/group is fine".
So, the problem is solved yet still remains my question:

Does 'addgroup' command exist at all in this release of freebsd?

obligedly and muchly so yours`
sehrguey