Problem with sending data to a server using sim900 with HTTP

[electronicsIUST]

Hello, I am trying to send some datas via post (or get) method in http from my sim900 module to a web page in a web server and then inserting it into a table in a database.
my web page is working good & i can post (or get) datas to it via browser in my pc and html forms
but I cant send datas from my sim900a module. Here is commands sequence for sim900. Can anyone help me please what to do?

AT+SAPBR=3,1,"APN","wholesale" OK

// Enable GPRS - this will take a moment or two
AT+SAPBR=1,1 OK

// Check to see if connection is correct and get your IP address
// (I hid mine here, but you'll get a real IP back)
AT+SAPBR=2,1 +SAPBR: 1,3,"0.0.0.0"
OK

// Enable HTTP mode
AT+HTTPINIT OK

// Set HTTP profile identifier
AT+HTTPPARA="CID",1 OK

// Put in the URL of the PHP webpage where you will post -
// the URL below is a test server so you can use it in testing
AT+HTTPPARA="URL","http://posttestserver.com/post.php"
OK

// Tell the SIM900 how much data you'll send (18 bytes here)
// and how long to wait for a time-out (10,000 ms here)
AT+HTTPDATA=18,10000 DOWNLOAD

// Key in the data you want to send after you get the "DOWNLOAD" prompt.
vdc=12&adc=3&rel=8 OK

// Post the data - wait a second for the response
AT+HTTPACTION=1 OK
+HTTPACTION:1,200,142

// Read the response - www.posttestserver.com will give you a
// URL where you can confirm that it's working
AT+HTTPREAD +HTTPREAD:142
OK

// Close the HTTP connection
AT+HTTPTERM