this box comes up asking for user name (admin) and password (admin)
wrong username & password for the telnet session. Username is most likely ‘root’, password is whatever you assigned at the time of unslinging.
This from the unslung readme file:
9) Verify that you can log into the NSLU2 by going to the web GUI “Manage Telnet”
page, enable the telnet service, then telnet in as the root user, with the
password you entered when you performed the “unsling” operation.
Hope that helps!