For same packet server's behaviour is different for .bin and for .out file

Hi, We develop one sip stack in VX-Works platform ,same code is working for .out hard phone but for .bin phone it is not working.In .bin for first register request it sends 401 unouthorized then we send resister with proper authorization but then also it is sending 401.But for same register request packet for .out phone receves 200ok response from same server. Regards, Supti