Using SIM900 GPRS shield to send sms

Hi,

I'm using a SIM900 GPRS shield V1.0 in my project. I am following this link to send an SMS using AT commands http://www.seeedstudio.com/wiki/GPRS_Shield_V1.0 I get correct responses for all the AT commands but when I send hex 1A after typing the message, it responds with "ERROR". Kindly help.

I think you can't send Control Z from the Serial Monitor make it in your code

Serial.println((char)26); or Serial.write(0x1A);