Yes - there is an IIS conenction timeout in IIS 5.0 and 4.0.
Most likely, however, the site you're connecting to uses a Program to host the site such as Serv-U or Cute FTP, etc. Those have greater control of connection features, and also have timeouts for Idle, and connection duration.
Depending on the site - many FTP hosts use an Idle timeout or Connection timeout for anonymous users, but no timeouts set for authenticated users.
In either case - I highly doubt the problem can be corrected by doing anything on your machine. I am 99% sure it is either your ISP doing it, or the remote FTP site disconnecting you.
You said you've tried it many times - was that connecting to the SAME FTP site, or different ones? If you get disconnected from the Internet - and not just the FTP site...it's your Dial-Up settings or ISP disconnecting you.
What ISP are you using?
Pbxman
Systems Administrator
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