Ii had the same problem for a while..
1. Make sure you're in DEV mode.
2. Get all the files listed in the thread at TreoCentral and look for WebOS Quick Install v1.4. Ya want Orca, Novacom, Quickinstall and WebOSDoctor files. Sorry but PreCentral won't let me post the link..
3. Run the Orca utility.
4. Double click on the "Safely Remove Hardware" icon on bottom righthand of your task toolbar (Icon should appear when you plug in your device).
5. Check the "Display Device Components" box in the "Safely Remove Hardware" dialog box.
6. Open the "Web OS Quick Install app and click FILE, OPTIONS..
7. Click the "Attempt Novacom (re)installation"..
Now for me, I have to watch the "Safely Remove Hardware" dialog while plugging in my Pre.. IF Novacom is listed along with the USB Mass Storage Device list for your PRE then you're good to go. I sometime have to stop the service, unplug then replug several times before Novacom is listed..
Why? I don't know.. But for the most part, once I got in, i installed FileCoaster and I don't require WebOSQuick install anymore.. For the most part..
It's a lot and it might not work for you, but this the world I had to live in to get it to work. That said,, ahem,, uhh ,, welcome to my world..