I am using the china E71 which is a dual SIM phone, it is the china phone with great and advance functionality,2 SIM can be used in phone, both are gsm sim. Its SIM1 is working properly. and SIM2 giving the error message "Invalid SIM" when we insert the SIM in SIM2 Holder. what can be the issue related with and what is the solution for such problem. please suggest me the proper solution which can solve the problem.