Thanks jdenny - that fixed the problem. I'm now getting the same errors as you if I don't add the correct command line flags - something like that would be useful to have in.

Edit: I ran the script against my router from the outside and it says that port 23 is open (telnet) but Shield's Up at grc.com disagrees with this and says that the port is stealthed (as is port 80 - but pyscan says that this is closed).