Problem in SIM900 GPRS connection
The problem (I believe) is that half way through your program you switched from using println() to using print(), thus the commands from that point on aren't being executed until right at the end where you switch back to println(), so the whole of the text you send from point 3 onwards is being run as one single command - which of course is in the wrong format:


  AT+SAPBR=3,1,"CONTYPE","GPRS"AT+SAPBR=3,1,"APN","internet"AT+SAPBR=1,1AT+HTTPINITAT+HTTPPARA="URL","xx.xx.xx.xx/my/web/site"AT+HTTPDATA=100,1000AT+HTTPREAD