GSM Shield v.2 + Arduino UNO... some problem!!!

Hi,
I buyed this shield board: http://arduino.cc/en/Main/ArduinoGSMShield
with external antenna connector.
I have an Arduino UNO board.
I plugged shield on Arduino board and with Arduino IDE v1.0.5 I tryed to use a GSM library with examples to try a sms send and receive.
While testing the program seems to freeze on initializing gsm in .begin method. I attached an image to focus the poi of stop…
Could someone help me, please?

just an information... PINNUMBER was set to "" due to not set sim's pin number. But I tryend with sim's pin number set and PINNUMBER correctly also but the results was not changed. I tried alto to power the boards with external power ... nothing changing...

help please!!!