I'm having trouble getting one Mac on my home LAN to talk to another - let's call them Red and Blue. Red can't connect via Finder (under Shared) to Blue. But Red can open a Screen Sharing session to Blue. Blue can open a Screen Sharing session to Red, and connect to Red via Finder. Both Red and Blue are using WiFi, connected to the same router. Both are running OSX Leopard, 10.5.8.
I have a third Mac I'll call Orange. Orange can connect via Screen Share or Finder to both Red and Blue.
What could be causing Red to have these issues connecting to Blue?