I have the same problem. I have to make multiple, anywhere from 5 - 20, attempts to try and upload or download. Eventually my laptop finds the iPronto, but it can be really frustrating after about the 15th try!
I am using XP. I am also using a "component" type wireless setup. Instead of an integrated router/hub/WAP, my setup uses all separate components. I wonder if Jax Beach Dave is using separate or integrated network hardware. I have spent several hours with both Philips support (isn't THAT fun!) and Linksys support. The Philips support people are using the Linksys setup (and smoking a little too much gange), but it is all integrated. I suspect that there is a timeout issue between all of these devices trying to handshake and negotiate a connection to the iPronto and on the occasional attempt that does get it, it simply is a "lucky shot" on my part catching something at exactly the right interval for the connection.
Good luck getting Linksys to step up to this issue. They have NO idea what an iPronto is and talk to you like you're crazy when you tell them that it is a remote control. I've actually gotten them to go to the Philips iPronto link on the 'net just to get them to see what I'm talking about... with no better luck.
I have my fingers crossed that some combination of a firmware upgrade and/or iProntoEdit upgrade will address the problem. Until then, I've virtually given up.