strange error on PHP 4.3.5 (works fine on 4.3.1)

Hey Guys,

I have a script that  runs fine on a local server (PHP 4.3.10) and a remote server (also 4.3.10) but on the clients server (4.3.5RC4) it gives me an undefined function error... very strange, heres the code;

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<?php
 ini_set('display_errors', 1);
 error_reporting(E_ALL &~E_NOTICE);
 
 include('header.php');
 include('menu.php');
 include('../config.php');
 
 function resampimagejpg($psize, $sourcefile, $pdestfile, $g_imgcomp) {
     $g_srcfile=$sourcefile;
     
     if(file_exists($sourcefile)) {
          //Get data from source image
          $g_is=getimagesize($sourcefile);
          $p = pathinfo($sourcefile);
          switch ($p['extension']) {
               case 'gif':
                    $img_src=imagecreatefromgif($sourcefile);
                    break;
               case 'jpg':
               case 'jpeg':
                    $img_src=imagecreatefromjpeg($sourcefile);
                    break;
               case 'png': // line 33, apparent errorneous line
                    $img_src=imagecreatefrompng($sourcefile);
                    break;
               default:
                    return false; //Can't handle other formats
          }
               //Create preview sized image
          if ($g_is[0] > $psize or $g_is[1] > $psize) { //Only shrink, don't enlarge to fit
               $g_fw=$psize;
               $g_fh=$psize;
               if(($g_is[0]-$g_fw)>=($g_is[1]-$g_fh)) {
                    $g_iw=$g_fw;
                    $g_ih=($g_fw/$g_is[0])*$g_is[1];
               } else {
                    $g_ih=$g_fh;
                    $g_iw=($g_ih/$g_is[1])*$g_is[0];
               }
               $img_dst=imagecreatetruecolor($g_iw,$g_ih);
               imagecopyresampled($img_dst, $img_src, 0, 0, 0, 0, $g_iw, $g_ih, $g_is[0], $g_is[1]);
          } else { //Just copy the image
               $img_dst = $img_src;
          }
          imageinterlace($img_dst, 1);
          imagejpeg($img_dst, $pdestfile, $g_imgcomp);
          imagedestroy($img_dst);
          return true;
     } else {
          return false;
     }
}
 
 
 //Check that there was actually an upload before proceeding
if (count($_FILES) > 0 and array_key_exists('image', $_FILES)) {
     if (is_uploaded_file($_FILES['image']['tmp_name'])) {
          if ($_FILES['image']['name'] != '')
          {
               $pic_name = "1_" . date("d_m_Y_H_i") . "_" . $_FILES['image']['name'];
          } else {
               exit; //Can't really do anything if we don't have a filename
          }
          $uploaddir = '../images/phones/';
          $thumbnaildir = '../images/phones/thumbs/';
          $sourcefile = $uploaddir.$pic_name;
          move_uploaded_file($_FILES['image']['tmp_name'], $sourcefile);
          $pdestfile = "{$thumbnaildir}tn_{$pic_name}";

          $g_imgcomp = $img_comp;
          $psize = $img_max_width;
          resampimagejpg($psize, $sourcefile, $pdestfile, $g_imgcomp);
     }
}
 
 if ($dbc = @mysql_connect($db_host, $db_user, $db_pass)) {
                                                if (!mysql_select_db($db_name)) {
                                                                        die('<p>Could not connect to the database because: <b>' . mysql_error() . '</b></p>');
                                                }
                        } else {
                                                die('<p>Could not connect to the database because: <b>' . mysql_error() . '</b></p>');
                        }
      
 $query1 = "SELECT * from phone_man ORDER BY name" or die(mysql_error());
 $r = mysql_query($query1) or die(mysql_error());
 $row = mysql_fetch_assoc($r);
        
 echo '<div class="main">';
 echo '
 <p><h1>Add a Phone</h1></p>';
 
 if (!isset($_POST['submit'])) {
 echo '
 <form name="add_phone" method="post" action="phones_add.php" enctype="multipart/form-data">
 <table width="80%" border="0">
 <tr>
 <td width="100">Name:</td>
 <td><input type="text" name="name" size="50" /></td>
 </tr>
 <tr>
 <td width="100">Manufacturer:</td>
 <td><select name="man">
 <option value="Select...">Select...</option>';
 do {
       echo'<option value="'.$row['name'].'">'.$row['name'].'</option>';
 }
 while($row = mysql_fetch_assoc($r));
 
 echo '</select></td>
 </tr>
 <tr>
 <td width="100">Features and Info:</td>
 <td><textarea name="body" cols="50" rows="10"></textarea></td>
 </tr>
 <tr>
 <td width="100">Image:</td>
 <td><input type="file" name="image" /></td>
 </tr>
 <tr>
 <td width="100">Price:</td>
 <td><input type="text" name="price" size="50" /></td>
 </tr>
 <tr>
 <td width="100">Network:</td>
 <td><input type="radio" name="network" value="cdma" /> CDMA<br />
 <input type="radio" name="network" value="gsm" /> GSM<br /></td>
 </tr>
 <tr>
 <td width="100"><input type="submit" name="submit" value="Add Phone" /></td>
 <td><input type="reset" name="reset" value="Clear Form" /></td>
 </tr>
 </table>
 </form>';
}
if (isset($_POST['submit'])) {
$p_name = addslashes($_POST['name']);
$p_man = addslashes($_POST['man']);
$p_body = addslashes($_POST['body']);
$p_image = addslashes($pic_name);
$p_price = addslashes($_POST['price']);
$p_network = addslashes($_POST['network']);

                        $query = "INSERT into phones (name, body, image, price, man, network) VALUES ('{$p_name}', '{$p_body}' , '{$p_image}', '{$p_price}', '{$p_man}' , '{$p_network}')";

                        if (@mysql_query ($query)) {
                                                header('Location: thanks.php');
                        } else {
                                                echo 'An error occured while entering the data, the error was ' . mysql_error() . ' and the query was ' . $query . '';
                        }
}
echo '</div>';
ob_end_flush();
include('footer.php');
?>
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The exact error is;

Fatal error: Call to undefined function: imagecreatefromjpeg() in /home/intouch/public_html/admin/phones_add.php on line 33

This is really urgent, any help is so muchly appreciated!!!!! :)

Christian