[plt-scheme] Windows: "Check for updates..." not working behind proxy?

Hello,

checking for updates does not work. I connect to Internet through a
proxy: could be this the issue? Anyway, I've configured the proxy into
Preferences, and requiring Planet packages works. I'm running Windows
XP SP3.

The error message says:

"Error could not connect to website.

(tcp-connect connection to download.plt-scheme.org port 80 failed (at
step 6: [italian message translation: Unable to establish connection.
Wrong reply or no reply from remote host.] errno=10060))"

Thanks.