I'm no linux maven but i have used smoothwall quite a bit. I am assuming that you are trying to log into the web interface (and not the console on the web interface) I've never seen that error message so my suggestions may not be relevant. the 3 most common error for logging into smoothwall are:
1. not specifying the correct host name (the default is smoothwall; the local lan IP address of the smoothwall should work i think).
2. not specifying one of the two possible ports, 81 or 445 (you should use 445 if possible for security's sake) from a box on the green lan (not the orange lan or externally through the red lan interface).
thus
http://smoothwall:81
or http
s://smoothwall:445
would access most default machines.
the alternative would be (substitute your green lan IP address here)
thus
http://10.1.1.1:81
or http
s://10.1.1.1:445
3. not using the correct user id / password. If you are trying to log into the web interface, the use "admin." If i am incorrect then, read below:
When you install smoothie, you create three users with distinct passwords
1.
root for loging into the command line at the smoothwall's own terminal or the web console noted above.
2.
admin for reviewing log files, doing post-installation configuration; and
3. some other user that i can't recall the name of used for accessing the dial - up which probably doesn't apply to you.