Ubuntu – Unable to SU with root: `/bin/bash: permission denied`

root@frankfurt:~# sudo adduser newuser
Adding user `newuser' ...
Adding new group `newuser' (1001) ...
Adding new user `newuser' (1001) with group `newuser' ...
Creating home directory `/home/newuser' ...
Copying files from `/etc/skel' ...
Enter new UNIX password: 
Retype new UNIX password: 
passwd: password updated successfully
Changing the user information for newuser
Enter the new value, or press ENTER for the default
    Full Name []: new
    Room Number []: 
    Work Phone []: 
    Home Phone []: 
    Other []: 
Is the information correct? [Y/n] y
root@frankfurt:~# su newuser
Cannot execute /bin/bash: Permission denied
root@frankfurt:~# 

Thanks.