"Internal authentication error."

This is generally a Windows NT 4.0/2000 error, and can be quite common

This usually refers to a username/password error on the users part, after you have checked, re-entered your username and password then you or your server admin might want to check these as well:

Most common NT problem is that under the Server Types tab you accidentally checked use encrypted password... which we aren't using.. so you might want to uncheck it.

You might also want to create another dialer/connectoid from scratch again.

This could possibly be a cached password in one of your .pwl files, but I'd suggest rebooting, and trying it once again after a fresh reboot.

Make sure there aren't any other applications running, pcanywhere, vpn's, etc..

As for drastic measures, unistalling the dial up networking altogether might work as an outside shot..