You must have got it wrong somewhere as it's still disabled (-1 at the end of line means = disable).
Code:
Domain Admins (S-1-5-21-842145922-2861567613-292939348-512) -> -1
It should read ...
Code:
Domain Admins (S-1-5-21-842145922-2861567613-292939348-512) -> ntadmins
Where 'ntadmins' is the account listed in /etc/group
Make sure you use 'net groupmap
modify ...' and not 'net groupmap
add ...'