OK, here's an update to the situation:

As a troubleshooting method, I disabled Norton and tried again: same thing.

As a further troubleshooting step, I downloaded and installed a trial version of Cute FTP Pro to rule out a problem with WS FTP Pro (which I uninstalled and reinstalled to no avail): Cute FTP Pro will not connect, either, giving "error 10061: no socket error".

This leads me to believe there's something wrong on the laptop, or else there is some setting that is not correct. I'm using port 21, as the program advised, and the settings are identical within WS FTP Pro on both machines (laptop and PC).

Does anyone have any ideas??????? This is most frustrating!