GSM SIM900A with Arduino UNO - AT Command error

hi, i have been trying to send sms when there is sensor output.

  1. sending the mobile no where sms needs to be sent via serial monitor of arduino uno.
  2. the number entered in serial monitor is saved in eeprom and eeprom data is feteched by gsm

i am getting error at : AT+CMGS = error - operation not allowed. please help me…

if i hardcode the mobile no (without using serial monitor) or use eeprom data , gsm is sending sms.