problem in modem interfacing with microcontroller

hi,

i m interfacing GSM modem to my microcontroller.i need to send sms through it.

i am using AT commands for that.the command to send sms (AT+ CMGS) must terminate with ctrl-Z.now in my program

AT , AT+CMGF = 1, AT+CMGS = mobile no. , "message to be sent " ctrl- Z /

the problem is : I connect my microcontroller and then switch ON the modem my program runs afterwards but SMS is not sent.but when i reset my microconroller board the SMS is sent. i am unable to find the reason.also i was suspecting the role of RTS pin but online documents show that it shuould be set high once only ....do i need to reset or do something with this pin when my program runs ?

plz suggest some way . suggestions are also invited if you suspect some other problem .