Why am I receiving groupadd/useradd errors when attempting to create a new account ?
Make sure your /etc/passwd and /etc/group file does not have the +i (immutable flag). You can check by running lsattr /etc/group and lsattr /etc/shadow. If it does have a +i flag, remove it by executing chattr -i /etc/passwd and/or chattr -i /etc/group.
It is also possible that your group shadow file is corrupt. To fix this, move /etc/gshadow to /etc/gshadow.corrupted and run grpconv to rebuild the file. You may need to remove grshadow.lock and/or group.lock if either exists.