I did manage to solve this problem.

Removed the link gshadow in /etc.
Copied gshadow from /KNOPPIX/etc to /etc
changed permissions of /etc/group and of /etc/gshadow
in code:
Code:
cd /etc
rm gshadow
cp /KNOPPIX/etc/gshadow gshadow
chmod 766 group
chmod 766 gshadow

After this I could run addgroup and adduser.

Thanks.