Problem with an update query

[Ugluth]

Hello there, i got a page where the administrator of the site is supposed to go and modify data about a customer. I got a dropdown to show the customer names, and after a customer is selected i show all his data on some textboxes. If the user hits the second submit its supposed to do an update query on the specified customer. Anyway, here's the code

 

<?php
session_start();
include("dbconn.php");
$customer = $_POST['menuCust'];
$query_menu=("SELECT Customer_ID, Customer_Name, Customer_Surname FROM customers");
$result_menu = mysql_query($query_menu) or die("Query failed: " . mysql_error());
$query_insert = ("UPDATE customers SET Customer_ID = '".$_POST['txtID']."', Customer_Name = '".$_POST['txtName']."', Customer_Surname = '".$_POST['txtSurname']."', Phone = '".$_POST['txtPhone']."', Join_Date = '".$_POST['txtDate']."' WHERE Customer_ID = '$customer'");
$query_customer = ("SELECT Customer_ID, Customer_Name, Customer_Surname, Phone, Join_Date FROM customers WHERE Customer_ID = '$customer'");
$result_customer = mysql_query($query_customer) or die ("Query failed: " . mysql_error());
if (isset($_POST['txtID'])) {
mysql_query($query_insert);
$update = "Update was succesfull";
}
?>

 

Here's the dropdown

<form id="frmMenu" name="frmCust" method="post" action="edit_customers.php">
  Customers
  <select name="menuCust">
  <option value=" "> </option>
    <?php
  while ($line = mysql_fetch_array($result_menu, MYSQL_NUM)) {
     echo "<option value=\"$line[0]\"";
 if ($_POST["menuCust"]==$line[0])
 	echo " selected" ;
 echo ">".$line[1]." ".$line[2]." </option>" ;
  }
  ?>
  </select>
  <input type="submit" name="Submit" value="Submit" />
</form>

 

And finally here are the textboxes

<form id="frmCust" name="form1" method="post" action="edit_customers.php">
<?php
if (isset($customer)){
while ($line = mysql_fetch_array($result_customer, MYSQL_NUM)) {
?>
  <p>Customer ID
    <input name="txtID" type="text" id="txtID" value="<?php echo $line[0]; ?>" />
  </p>
  <p>Name
    <input name="txtName" type="text" id="txtName" value="<?php echo $line[1]; ?>" />
  </p>
  <p>Surname
    <input name="txtSurname" type="text" id="txtSurname" value="<?php echo $line[2]; ?>" />
  </p>
  <p>Phone
    <input name="txtPhone" type="text" id="txtPhone" value="<?php echo $line[3]; ?>" />
  </p>
  <p>Join Date
    <input name="txtDate" type="text" id="txtDate" value="<?php echo $line[4]; ?>" />
      <input type="submit" name="Submit2" value="Submit" />
  </p>
<?php
}
}
?>
</form>
<?php
echo $update;
$update = " ";
mysql_free_result($result_customer);
mysql_free_result($result_menu);
?>

My problem is that it wont update even though the query works, when i used

if (!mysql_query($query_insert)) {
        die(mysql_error());    
    }else{
        $update= "Update was succesfull";
}

it did update. So any help with it please? thanks in advance!