The fact that some of the screens are "perfect" leads me to believe the problem is with the software rather than the hardware.

In case you didn't know, the firmware (Linux + music player + menus + fonts + ...) is downloaded from the Windows server when the Rio first boots up. The Linux boot image file is "C:\Program Files\Audio Receiver\receiver.arf". If the Linux image file is corrupted (say, in the fonts area), symptoms such as yours are possible.

I would suggest that you re-install the Audio Receiver software on your Windows machine, then unplug the Rio's power cord, count to ten, and plug it back in and turn it on (cold boot). Just turning off the power button doesn't actually force a cold reboot. In fact, if you run a lan trace while the Rio is turned off, you'll notice that it is still responding to queries from the Audio Manager on the Windows box!!!!! (UDP port 18678)

No guarantee, but that just might solve the problem....