RealVNC gives unknown message type 167

I'm trying to use the RealVNC viewer from a Windows machine to talk to a Mac running OS X 10.4.3 and Apple Remote Desktop. It almost works, and in fact one time it did work, but on every subsequent attempt, I get "unknown message type 167." The message comes up after I give the VNC password, and while the screen is initially drawing. Every other VNC viewer I've tried also fails to connect.