Why is my variable not coming back with the correct result?

Hi all,
I using the function mysql_insert_id(); to take the last created auto-numeber and poplulate another table with the same result. This works fine:
$member_main_last_id = mysql_insert_id();

//the next table
GetSQLValueString($member_main_last_id, "int"),

Now when I try to use this variable $member_main_last_id to post it to the next page it gives me a strange result. When I echo it to the page the correct figure might be say "55" but it prints "35", always 20 less than the actual figure! I can't understand this.

Here is the source of the page if someone could have a look.
Cheers,
D

<?php require_once('../Connections/reacha_new.php'); ?>
<?php
session_start();

function GetSQLValueString($theValue, $theType, $theDefinedValue = "", $theNotDefinedValue = "")
{
  $theValue = (!get_magic_quotes_gpc()) ? addslashes($theValue) : $theValue;

  switch ($theType) {
    case "text":
      $theValue = ($theValue != "") ? "'" . $theValue . "'" : "NULL";
      break;    
    case "long":
    case "int":
      $theValue = ($theValue != "") ? intval($theValue) : "NULL";
      break;
    case "double":
      $theValue = ($theValue != "") ? "'" . doubleval($theValue) . "'" : "NULL";
      break;
    case "date":
      $theValue = ($theValue != "") ? "'" . $theValue . "'" : "NULL";
      break;
    case "defined":
      $theValue = ($theValue != "") ? $theDefinedValue : $theNotDefinedValue;
      break;
  }
  return $theValue;
}

$editFormAction = $_SERVER['PHP_SELF'];
if (isset($_SERVER['QUERY_STRING'])) {
  $editFormAction .= "?" . htmlentities($_SERVER['QUERY_STRING']);
}

if ((isset($_POST["MM_insert"])) && ($_POST["MM_insert"] == "personal_reg")) {
  $insertSQL = sprintf("INSERT INTO member_main (mm_username, mm_full_address, mm_travel, mm_mem_type_id, mm_password, mm_native_town_id, mm_contact_nr, mm_contact_nr_alt, mm_email_add, mm_website_add, mm_lat, mm_long, mm_start_date) VALUES (%s, %s, %s, %s, %s, %s, %s, %s, %s, %s, %s, %s, now())",
                       GetSQLValueString($_POST['txt_username'], "text"),
                                 GetSQLValueString($_POST['txt_full_add'], "text"),
                                 GetSQLValueString($_POST['drop_travel'], "text"),
                                 GetSQLValueString($_POST['teacher_type'], "int"),
                       GetSQLValueString($_POST['txt_password'], "text"),
                       GetSQLValueString($_POST['Town'], "int"),
                       GetSQLValueString($_POST['txt_num1'], "int"),
                       GetSQLValueString($_POST['txt_num2'], "int"),
                       GetSQLValueString($_POST['txt_email_add'], "text"),
                       GetSQLValueString($_POST['txt_web'], "text"),
                       GetSQLValueString($_POST['latitude'], "double"),
                       GetSQLValueString($_POST['longitude'], "double"));

  mysql_select_db($database_reacha_new, $reacha_new);
  $Result1 = mysql_query($insertSQL, $reacha_new) or die(mysql_error());
}

$member_main_last_id = mysql_insert_id();



if ((isset($_POST["MM_insert"])) && ($_POST["MM_insert"] == "personal_reg")) {
  $insertSQL = sprintf("INSERT INTO member_per (mp_mem_id, mp_gender, mp_availability) VALUES (%s, %s, %s)",
                       GetSQLValueString($member_main_last_id, "int"),
                                 GetSQLValueString($_POST['select_gender'], "text"),
                       GetSQLValueString($_POST['txt_availabilty'], "text"));

  mysql_select_db($database_reacha_new, $reacha_new);
  $Result1 = mysql_query($insertSQL, $reacha_new) or die(mysql_error());
 
  $insertGoTo = "../Registration/reg6.php";
  if (isset($_SERVER['QUERY_STRING'])) {
    $insertGoTo .= (strpos($insertGoTo, '?')) ? "&" : "?";
    $insertGoTo .= $_SERVER['QUERY_STRING'];
  }
  $_SESSION['member_id'] = $_POST['member_id'];
  $_SESSION['distance'] = $_POST['distance'];
  $_SESSION['latitude'] = $_POST['latitude'];
  $_SESSION['longitude'] = $_POST['longitude'];
  $_SESSION['Town'] = $_POST['Town'];
  header(sprintf("Location: %s", $insertGoTo));
}


 //require_once('../Connections/reacha_new.php'); ?>
<?php
mysql_select_db($database_reacha_new, $reacha_new);
$query_rscounty_town = "SELECT county.c_county_id, county.c_county_name, town.t_town_id, town.t_town_name, town.t_lat, town.t_lon, town.t_county_id FROM county, town WHERE town.t_county_id = county.c_county_id";
$rscounty_town = mysql_query($query_rscounty_town, $reacha_new) or die(mysql_error());
$row_rscounty_town = mysql_fetch_assoc($rscounty_town);
$totalRows_rscounty_town = mysql_num_rows($rscounty_town);
?><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
<title>Personal Registration Page</title>
<style type="text/css">
<!--
.style1 {font-size: 10px}
-->
</style>
<script type="text/javascript">
function showHideRow(selectboxValue, rowID) {
  if(selectboxValue == "yes") {
    document.getElementById(rowID).style.display = '';
  } else {
    document.getElementById(rowID).style.display = 'none';
  }
}
</script>
</head>

<body>
<form id="personal_reg" name="personal_reg" method="POST" action="<?php echo $editFormAction; ?>">
<?php echo $_POST['drop_travel'] ?>
  <label for="textfield">Personal Details <br />
  <br />
  </label>
  <table width="428" border="1">
    <tr>
      <td width="191"><label for="lbl_username">Username<br />
      <span class="style1">(this is what will be displayed to the users) </span></label></td>
      <td width="221"><input type="text" name="txt_username" id="txt_username" /></td>
    </tr>
    <tr>
      <td><label for="lbl_gender">Gender</label></td>
      <td><select name="select_gender" id="select_gender">
        <option value="male">Male</option>
        <option value="female">Female</option>
      </select></td>
    </tr>
    <tr>
      <td><label for="lbl_password">Password</label></td>
      <td><input type="password" name="txt_password" id="lbl_password"  /></td>
    </tr>
    <tr>
      <td><label for="lbl_re_password">Re-enter Password</label></td>
      <td><input type="password" name="txt_re_password" id="lbl_re_password" /></td>
    </tr>
    <tr>
      <td>Are you willing to travel to students? </td>
      <td><label for="lbl_travel"></label>
        <select name="drop_travel" id="lbl_travel" onchange="showHideRow(this.options[this.selectedIndex].value, 'travel2');">
          <option value="no">No</option>
          <option value="yes">Yes</option>
        </select>      </td>
    </tr>
    <tr id="travel2" style="display:none;">
      <td>Approx how many km are you willing to travel? </td>
      <td><label for="lbl_distance"></label>
        <select name="distance" id="distance" >
          <option value="5">5</option>
          <option value="10">10</option>
          <option value="20">20</option>
          <option value="50">50</option>
          <option value="75">75</option>
        </select>
      </td>
    </tr>
    <tr>
      <td><label for="lbl_avail">Availability</label></td>
      <td><textarea name="txt_availabilty" cols="34" rows="3" id="lbl_avail"></textarea></td>
    </tr>
  </table>
 

    <p>&nbsp;</p>
    <p>Location Details: </p>
    <table width="400" border="1">
      <tr>
        <td>Select your County </td>
        <td><select name="County" id="County" onchange="TCN_reload(this)">
          <option selected="selected">County</option>
        </select></td>
      </tr>
      <tr>
        <td>Select your Town</td>
        <td><select name="Town" id="Town" onchange="TCN_reload(this)">
          <option selected="selected">Town</option>
        </select></td>
      </tr>
      <tr>
        <td><label for="lbl_full_add">Full Address (*)</label></td>
        <td><textarea name="txt_full_add" cols="30" rows="3" id="label9"></textarea></td>
      </tr>
      <tr>
        <td colspan="2"><div align="center">Click <a href="../map/sfliveaddpt.php" target="myChildWindow">here</a> to add your exact address on a map </div></td>
      </tr>
    </table>
   
    <p>
      <script language="JavaScript" type="text/javascript">
TCN_contents=new Array();
TCN_tempArray=new Array();
TCN_counter=0;
function TCN_addContent(str){
      TCN_contents[TCN_counter]=str;
      TCN_counter++;
}
function TCN_split(){
      TCN_arrayValues = new Array();
      for(i=0;i<TCN_contents.length;i++){
            TCN_arrayValues[i]=TCN_contents[i].split(separator);
            TCN_tempArray[0]=TCN_arrayValues;
      }
}
function TCN_makeSelValueGroup(){
      TCN_selValueGroup=new Array();
      var args=TCN_makeSelValueGroup.arguments;
      for(i=0;i<args.length;i++){
            TCN_selValueGroup[i]=args[i];
            TCN_tempArray[i]=new Array();
      }
}
function TCN_makeComboGroup(){
      TCN_comboGroup=new Array();
      var args=TCN_makeComboGroup.arguments;
      for(i=0;i<args.length;i++) TCN_comboGroup[i]=findObj(args[i]);
}
function TCN_setDefault(){
      for (i=TCN_selValueGroup.length-1;i>=0;i--){
            if(TCN_selValueGroup[i]!=""){
                  for(j=0;j<TCN_contents.length;j++){
                        if(TCN_arrayValues[j][(i*2)+1]==TCN_selValueGroup[i]){
                              for(k=i;k>=0;k--){
                                    if(TCN_selValueGroup[k]=="") TCN_selValueGroup[k]=TCN_arrayValues[j][(k*2)+1];
                              }
                        }
                  }
            }
      }
}
function TCN_loadMenu(daIndex){
      var selectionMade=false;
      daArray=TCN_tempArray[daIndex];
      TCN_comboGroup[daIndex].options.length=0;
      for(i=0;i<daArray.length;i++){
            existe=false;
            for(j=0;j<TCN_comboGroup[daIndex].options.length;j++){
                  if(daArray[i][(daIndex*2)+1]==TCN_comboGroup[daIndex].options[j].value) existe=true;
            }
            if(existe==false){
                  lastValue=TCN_comboGroup[daIndex].options.length;
                  TCN_comboGroup[daIndex].options[TCN_comboGroup[daIndex].options.length]=new Option(daArray[i][daIndex*2],daArray[i][(daIndex*2)+1]);
                  if(TCN_selValueGroup[daIndex]==TCN_comboGroup[daIndex].options[lastValue].value){
                        TCN_comboGroup[daIndex].options[lastValue].selected=true;
                        selectionMade=true;
                  }
            }
      }
      if(selectionMade==false) TCN_comboGroup[daIndex].options[0].selected=true;
}      
function TCN_reload(from){
      if(!from){
            TCN_split();
            TCN_setDefault();
            TCN_loadMenu(0);
            TCN_reload(TCN_comboGroup[0]);
      }else{
            for(j=0; j<TCN_comboGroup.length; j++){
                  if(TCN_comboGroup[j]==from) index=j+1;
            }
            if(index<TCN_comboGroup.length){
                  TCN_tempArray[index].length=0;
                  for(i=0;i<TCN_comboGroup[index-1].options.length;i++){
                        if(TCN_comboGroup[index-1].options[i].selected==true){
                              for(j=0;j<TCN_tempArray[index-1].length;j++){
                                    if(TCN_comboGroup[index-1].options[i].value==TCN_tempArray[index-1][j][(index*2)-1]) TCN_tempArray[index][TCN_tempArray[index].length]=TCN_tempArray[index-1][j];
                              }
                        }
                  }
            TCN_loadMenu(index);
            TCN_reload(TCN_comboGroup[index]);
            }
      }
}
function findObj(n, d) { //v4.01
  var p,i,x;  if(!d) d=document; if((p=n.indexOf("?"))>0&&parent.frames.length) {
    d=parent.frames[n.substring(p+1)].document; n=n.substring(0,p);}
  if(!(x=d[n])&&d.all) x=d.all[n]; for (i=0;!x&&i<d.forms.length;i++) x=d.forms[i][n];
  for(i=0;!x&&d.layers&&i<d.layers.length;i++) x=findObj(n,d.layers[i].document);
  if(!x && d.getElementById) x=d.getElementById(n); return x;
}
TCN_makeSelValueGroup("","");
TCN_makeComboGroup("County","Town");
 var separator="+#+";
<?php do{?>
TCN_addContent("<?php echo $row_rscounty_town['c_county_name']; ?>+#+<?php echo $row_rscounty_town['c_county_id']; ?>+#+<?php echo $row_rscounty_town['t_town_name']; ?>+#+<?php echo $row_rscounty_town['t_town_id']; ?>");
<?php } while ($row_rscounty_town = mysql_fetch_assoc($rscounty_town)); ?>
TCN_reload();

      </script>
    </p>
   
    <p>
      <label for="lbl_lat">Latitude</label>
      <input type="text" name="latitude" id="latitude" value="<?php echo htmlspecialchars($_POST['new_lat']);?>" />
    </p>
  <p>
      <label for="lbl_long">Longitude</label>
      <input type="text" name="longitude" id="longitude" value="<?php echo htmlspecialchars($_POST['new_lon']);?>" />
  </p>
  <p>Contact Details: </p>
  <table width="400" border="1">
    <tr>
      <td><label for="lbl_num1">Contact Number</label></td>
      <td><input type="text" name="txt_num1" id="txt_num1" /></td>
    </tr>
    <tr>
      <td><label for="lbl_num2">Contact Number 2 * </label></td>
      <td><input type="text" name="txt_num2" id="txt_num2" /></td>
    </tr>
    <tr>
      <td><label for="lbl_email_add">Email Address</label></td>
      <td><input type="text" name="txt_email_add" id="txt_email_add" /></td>
    </tr>
    <tr>
      <td><label for="lbl_web_add">Website Address * </label></td>
      <td><input type="text" name="txt_web" id="txt_web" /></td>
    </tr>
  </table>
  <p>&nbsp;</p>
  <p>
    <label for="Submit">Proceed to Subject Information</label>
    <input type="submit" name="Submit" value="Proceed" id="Submit" />
    <label for="label10"></label>
</p>

<input type="hidden" name="MM_insert" value="personal_reg"/>
<input type="hidden" name="teacher_type" value="<?php echo $_POST['cat_select'] ?>"/>
<input type="hidden" name="member_id" value="<?php echo $member_main_last_id ?>"/>
<?php echo $member_main_last_id ?>
</form>
</body>
</html>
<?php
mysql_free_result($rscounty_town);
?>