I am confused as Calibre does not run on an iPod or iPad
I suspect you really mean you are using Stanza? If so this is really a Stanza (or iOS) problem which is unfortunate as Stanza is no longer being maintained or updated as far as I can see. However in my experience you get a far more reliable connection from Stanza if you use the IP address:Port of the computer running the Calibre Content server rather than relying on Bonjour to locate it.