Yeah, it was just one of those things: read the manual first. The problem was in my chap-secrets file, where the host names were not properly entered. When I did this (although it was a bit of problem getting the host name of my provider), everything worked on the first try!
I admit, although I'm a long-time UNIX administrator, I don't have much experience with pap/chap authentication, so I was a bit confused. Now - it's all clear.
Anyway, thanks, Charlie, for trying to help.
Vanco