Error while sending SMS through Airtel network

Hi,

I have developed a IVR system using Arduino uno and GSM SIM900A. It woks well, except for a small glitch. I am having problem in sending SMS, when the SIM is Airtel. SMS works well with other SIMs such as Aircel, Vodafone, BSNL etc.

Did any of you face similar issue. Appreciate your guidance.

Pals.