Arduino Duemilanove + Java

I have what hopefully is a simple question about interfacing my Arduino with Java. I downloaded the code from the Playground section of the website, brought it into Eclipse, added the .jar and .dll to my build path, hit compile, and voila, everything my arduino sent via the serial port showed up in Eclipse's console. Worked like a charm with very little work on my part.

Unfortunately it seems that that was too good to be true. For some reason when I ran the same code the next day, I got a popup which was a Configure window for my USB ports. It listed numbers 1-128 and asked me to check off which ones were valid ports and hit save. Because my Arduino was plugged into Port 4, I checked that one and hit save. Nothing happened. The console showed the location of a Preferences file which was apparently being saved to, but there was no "Ok" or "Next" button. I hit the X to get out of the window, and it went away, but the console didn't show my Arduino's output any more.

What's going on? What is this GNU Port Properties window? And how come it won't read the port any more? If anyone else has run into this problem please let me know. I can provide screen shots if you think that will help.

(Just for reference, I'm running Windows 7 64 bit, although I should state again that the code worked fine the first time).