UDP with wifi shield hangs

Whenever I call UDP.write my application hangs. I've tried these tips in setup:

pinMode(4,OUTPUT);
digitalWrite(4,HIGH);

but nothing makes a difference. The only thing I haven't tried is upgrading the shield firmware (because I lack the cable).

UNO rev 3
Arduino Wifi Shield
IDE 1.5.6r2

You need to upgrade the shield firmware.

The earlier library did not support UDP
The later library does not support the earlier firmware.