GPRS with SM5100B

Thanks for your advices, my code it's already working, but i have some problems with the command AT+DATATSEND, i want to send mesages from my smb5100b but when i use this command I recieve error messages like CMR: ERROR 4, and when i put the comand like this

AT+DATATSEND= 1,1

i have this answer

and my device doesn't receive any other command

i have the same problem when i write this comand on arduino with this code

cell.print("AT+DATATSEND= 1,1")

could you help me please? thanks!