cannot access on some web sites

[hadrien001]

From few days I can't access to some web site like www.knoppixfr.org and I obtain this message when I try to connect on it:
Forbidden

You don't have permission to access / on this server.

Apache/1.3.27 Server at www.knoppixfr.org Port 80

I use a mtu=1400 on my lan connection
but may be it's just a config file default.
I will be very agree if somebody can help me.
francis