Screen won't work after 'su non-root-user'

["Sean O'Dell" <sean@celsoft.com>]

If I ssh into a machine as root, then su to a non-root user, then try to run
screen, I get this error:

        Cannot open your terminal '/dev/pts/0' - please check.

I also get this error if I log into my local machine as root, then su to a
non-root user and try to run screen.

However, if I either ssh into the remote machine, or log into the local
machine, directly as the non-root user, screen works fine.

Both the local and remote machine are updated with the latest packages from
Debian, both unstable and testing.

It's seems that, somehow, when I su to a non-root user, something changes
that prevents screen from working.

Any ideas?

        Sean O'Dell