Pic18F4550 + SIMCOM SIM900D GSM/GPRS

[tacbanon]

It locks up just right after it performs the first AT command..the same result when I rearrange the code.

main:
PORTB = 0            ' PORTB lines low to read buttons
TRISB = %11111000 
;gosub CLR_SCRN
GOSUB GSM_SIGCHECK
;gosub CLR_SCRN
gosub GSM_MODEL 

pause 260   ' pause to avoid sending repetition

;goto main
End   'End program

it perform GOSUB GSM_SIGCHECK then after it it never performs the gosub GSM_MODEL correctly and calls GSM_CHECK_ERR:
I also tried to interchange the sequence but the same results. It performs the GOSUB GSM_MODEL but failed to execute GOSUB GSM_SIGCHECK correctly.

/tacbanon