Problem seeduino GPRS SHIELD SIM900 + Arduino Uno

I’m trying to send sms from my Arduino Uno connected with Seeduino GPRS Shield SIM900.
Ive done all the procedure reported on this wiki by seeduino:

and everything was ok till I tried to type the following command to send the sms on the sscom.3.2:
AT + CMGS = “+393311234567” --> ERROR

But it reports ERROR as you can see in attach file.
(you can find in attach a screen shot)

I have also tried to modify the message center, but I’ve an error also with that instruction.
AT+CSCA="+393916263333" --> ERROR

I don’t really know what I can do.
Anyone can help me?

Thank you in advance

Hi,please have a try to call a native phone

such as AT + CMGS = “Phone num”

and please confirm the protocol of your phone.

“CMGS”、“CSCA” , or others?