This problem is resolved via security group defining NMSSI user with SUPERUSER privilege.
The error message breaks down as:
Errno = X'0000006F' = EACCES (Permission is denied).
ErrnoJr = X'xxxx7209' = JRIOCTLACCESSAUTHORIZATION
(The user does not have Access Authority for the requested IOCTL).
So the IOCTL has security requirements.
When the 'UNIX=YES' SOLVE SSI parameter is specified, the Userid assigned to the SOLVE SSI Address Space must be a SUPERUSER, i.e. UID(0) in the OMVS segment.