I deleted all my Arduino files including the ones in the user\documents\ directory (I hate it when files are automatically installed there), downloaded the Arduino compiler from Arduino.cc compiled and uploaded the W5100 sketch. Everything seems to be working fine now. Also Ping says it is OK. Thanks again for your simple and clear instructions.
The only thing I do not understand is why the Setup and Loop section are empty and I wonder how I can use the gateway itself with a simple sensor. If would like to first test it with my Homey before I start buying all kinds of sensors.