Hi!

I have the same phenomenon - and the solution - At least with my Fritz!Box Fon the solution works.
My DSL-Modem (Fritz!Box Fon) wants to have an unique identifier for the pppoe-connection. Therefor the pppoeconf - script needs to be modified.
The script is in /usr/sbin
The script is on CD-ROM - so can't be modified directly. copy it first into the home directory.
1. Open a Root-Shell
2. cp /usr/sbin/pppoeconf .
3. joe pppoeconf (edit the script for example with joe)
4. find the line containing "($DISCOVERY_PROGRAM -A -I $iface"...
5. change it to "($DISCOVERY_PROGRAM -A -U -I $iface"...
6. save and exit with control-k-x
7. run the script with ./pppoeconf
8. now it should work!

Hope this helps,
Pfeffer.