ethernet shield e led

Ciao,
no riesco a capire perchè con questo pezzo di codice il led che ho collegato tra il pin 13 e gnd si accende

byte mac[] = { 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED }; //physical mac address
byte ip[] = { 192, 168, 10, 15 };                  // ip in lan
byte gateway[] = { 192, 168, 10, 1 };                  // internet access via router
byte subnet[] = { 255, 255, 255, 0 };                   //subnet mask
Server server(80);                                      //server port
byte sampledata=50;            //some sample data - outputs 2 (ascii = 50 DEC)             
int ledPin = 13;  // LED pin
String readString = String(30); //string for fetching data from address
boolean LEDON = false; //LED status flag
void setup(){
//start Ethernet
  Ethernet.begin(mac, ip, gateway, subnet);
  pinMode(ledPin, OUTPUT);  
  digitalWrite(ledPin, LOW);    // set the LED OFF
//enable serial datada print  
  Serial.begin(9600);
}
void loop(){
// Create a client connection
digitalWrite(ledPin, LOW);
Client client = server.available(); 
}

Se tolgo Client client = server.available(); il led rimane spento....
qualche dritta?
Grazie

ciao,
se guardi la pagina dello shield:
http://www.arduino.cc/en/Main/ArduinoEthernetShield
trovi:

Arduino communicates with both the W5100 and SD card using the SPI bus (through the ICSP header). This is on digital pins 11, 12, and 13 on the Duemilanove and pins 50, 51, and 52 on the Mega. On both boards, pin 10 is used to select the W5100 and pin 4 for the SD card.

I pin 10,11,12 e 13 sono riservati per l'ethernet shield.
Led (o altro) attaccati a questi pin comportano un malfunzionamento dello shield stesso, nonchè risultati imprevedibili :o

M

Grazie mille! Tutto ok.