I too have had this problem. I'm running on Windows 2000 Advanced Server with about 9,200 songs. RRR 0.7.10 worked great as long as I was playing from the unit. I wanted to check out the Web server and after a few clicks, the unit freezes and no longer responds to any Web requests. This is without even playing a song.
I also noticed that HPNA doesn't work with this (or any other other players I've been trying.) The Rio finds the music server and then just sits there. I have two Rios with one of the able to connect to my 10/100 network. Once I switched over, the Rio started working. The one on the HPNA - never starts up.
I'm actually pretty excited about playing with something different on my Rio - especially the streaming audio from ShoutCast. What's also cool is that with a PocketPC (like Toshiba's e740) you can wirelessly surf to admin Web pages and view and control the Rio. (Much cooler than the two-way Sony Remote Controllers).
I'm anxious to see if version .80 will solve the Rio locking up after hitting the Web interface. I too use a lot of M3U lists as one of the other repliers listed. With 9,200 songs... You have to.