RAS Async Adapter error - no dial-up

[Alessio]

On my Toshiba Satellite A60, WinXP Home, when I try to connect to the
Internet through the modem, I get Error 6: invalid handle, and after
some attempts I get Error 50: all devices connected / request not supported.
The modem works fine: diagnostics say ok, it dials correctly the number,
negotiates user and password. Then I get the error 6 and 50.
The Toshiba disgnostic tool says:
- modem test pass
- network test fail
I can connect to another PC through the cable LAN, and I can use its
internet connection.

Device Manager / Network / RAS Async Adapter shows an error (black
exclamation point on a yellow field).

I have:
- sarched through the FAQ and the knowledege base
- uninstalled / re-installed modem
- updated winXP via windows update
- updated bios / modem / network drivers from Toshiba
- tried to uninstall RAS Async Adapter, but no chance, says it may be
necessary for boot-up
I have found on the internet this tip to uninstall and re-install the
RAS Async Adapter:
http://forums.practicallynetworked.com/showthread.php?t=6781
I have followed the instructions and executed RArepair.exe.
It uninstalls and reinstalls the the RAS Async Adapter, but RAS is still
in error.

Any suggestions?
Thanks in advance
Alessio - Italy