ftp/telnet/ssh root login is disabled in newnigam2 oe2.6 by default
you have to login with the user newnigma2 instead

Anleitung zum Newnigma2 Image (OE2.5 basiert und neuer)

root is not disabled for telnet. root is only disabled for ssh.
Set a password for root via gui and you can login with root via telnet.

graphical user interface

Once again:
After flashing a clean Newnigma2 OE2.6 based image:

root with telnet is working by default. By default theres no password set for user root.

root with ssh doesnt work period. For ssh you have to use the user newnigma2 with password DreamOne.
The user newnigma2 has sudo rights, which you have to use in the cli.

So if you use the user root via telnet, theres no difference to the OE2.5 based image. If if doesnt work, you most likely forgot to disable "Backup current settings before flashing" und "Restore settings after flashing" before flashing, or something else went wrong.