If you type "man pppd" and the enter key at a terminal you will have alot of reading material.
"19 We failed to authenticate ourselves to the peer" is the exact defination from the manual.

Sometimes this means that noauth has not been selected in kppp or in the /etc/ppp/options file.
There are other files that could be causing this problem too. You can try putting "noauth" in the kppp
options set up. Usually this option is already selected though. If that doesn't fix the problem you might
want to re-do your pppd configuration

starting over with configuration.
1) delete any dialout accounts you have. You should check your /etc/ppp files and delete
any files with your isp name on/in them. If you used "pppconfig" to set up your
internet you might want to delete old connections that way.
2) Use "pppconfig" to set up your modem and connection. This creates the correct files
in /etc/ppp To use pppconfig just type that. as root, at a terminal.
3) set up kppp for ease of dial out.

Good luck