A problem which still exists in all versions of Knoppix is when trying to bring up ppp as the normal knoppix user and the noauth option is set.
When using kppp to set up a new internet connection it always adds the "noauth" option for ppp. Now when trying to call the provider ppp terminated after a successfull call and kppp brings up a dialog with error number 1 or number 2. Nobody can interpret these error number unless trying calling ppp up in a terminal window to see the log.
There are 2 ways to "solve" this problem:
a) bring ppp up as root (not good)
b) start kppp. open the dialog for the ppp-options and delete the noauth option. DON'T open this dialog again, because the noauth option will always be added per default! I don't know why this is so. Maybe a bug in kppp. Then bring ppp up.
So there should be added a workaround for this problem.