Running 4D Client in classic mode under Mac OS X sometimes results in the connection being dropped. What may cause this is the Classic environment going to sleep and letting the client time out. The controls for Classic sleep can be found in the "System Preferences" in Mac OS X. Choose "Classic" and click on the "Advanced" tab. This is where the sleep control is located. Set the sleep control to "Never" and classic will remain awake through even the most boring connections.