I am working with PHPExcel and I keep on getting this error:

The file PHPExcel_Shared_String.php is missing in the includes folder.

It is not showing up as a fatel error or anything like that. It is just printing out on the screen. I am using PHPExcel Version 1.8.0.

mypage.php

include('../../../assets/phpexcel/Classes/PHPExcel/IOFactory.php');

$allowedExts = array("xlsx");
				$temp = explode(".", $_FILES["file"]["name"]);
				$extension = end($temp);
				if (($_FILES["file"]["size"] < 4194304) && in_array($extension, $allowedExts)){
					if ($_FILES["file"]["error"] > 0){
						echo "Return Code: " . $_FILES["file"]["error"] . "<br>";
					}
					move_uploaded_file($_FILES["file"]["tmp_name"], "./Upload/" . $_FILES["file"]["name"]);
					$filename = $_FILES["file"]["name"];

					$b = "INSERT  INTO uploaded VALUES ('', '".$filename."', NOW(), '".$session->username."')";
					$b1 = $minidb->prepare($b);
					$b1->execute();

					//Begin Database input
					// Include our library for reading Excel files
				    include('../../../assets/phpexcel/Classes/PHPExcel/IOFactory.php');
					$file = "..//Upload/".$filename;

					// Let's try to read the data
					try {   
						$php_excel = PHPExcel_IOFactory::load($file);
					}
					catch(Exception $e) {
						die('Error loading file "'.pathinfo($file, PATHINFO_BASENAME).'": '.$e->getMessage());
					}

					$sheet_data = $php_excel->getActiveSheet()->toArray(null,true,true,true);

					// Shift our first result, as that is our column data
					$columns = array_shift($sheet_data);

					// Map our column keys
					$column_map = array();
					foreach ($columns as $key => $column) {
						$column_map[$column] = $key;
					}

					// Go through our entire sheet and put in our data array to get ready for MySQL import
					$data = array();
					foreach($sheet_data as $sheet) {

						// Only add if our source is HCC
						if(!empty($sheet[$column_map['Serial']])) {
							//Setting the script for checking Case and T
							$serial = $sheet[$column_map['Serial']];
							$crown = $sheet[$column_map['crown']];
							//Changing all lowercase letters to Uppercase.
							$userial = strtoupper($serial);
							$ucrown = strtoupper($crown);

							//Checking for "T" infront of Serial and Crown
							$str_pos = strpos ($userial, 'T');
								if($str_pos !== false && $str_pos === 0){
									 $gserial = $userial;
								}else{
									$gserial = "T".$userial;
								}
							$str_pos2 = strpos ($ucrown, 'T');
								if($str_pos2 !== false && $str_pos2 === 0){
									 $gcrown = $ucrown;
								}else{
									$gcrown = "T".$ucrown;
								}

							$data[] = array(
								'serial'	=> $gserial,
								'crown'		=> $gcrown,
								'description'		=> $sheet[$column_map['Description']],
								'size'		=> $sheet[$column_map['Size']],
								'load_wk'	=> $sheet[$column_map['wk']],
								'bitdate'  => $sheet[$column_map['date']],
								'partnumber'  => $sheet[$column_map['Part number']],
								'stockpoint'  => $sheet[$column_map['STOCKPOINT']],
								'source'  => $sheet[$column_map['Source']],

							);
						}
						else{ echo '<h1>OOPS</h1>';}

					}

					// Go through each order and create batches of 100 inserts. This is better than doing a query for every
					// single order, and should keep it running efficiently.
					$sql_batch = array();
					for($i = 0; $i < count($data); $i++) {

						// Add our insert line for every 100
						if($i % 100 == 0) {
							$sql_batch[floor($i / 100)] = "INSERT IGNORE INTO bits (`" . 
									implode("`,`", array_keys($data[0])) . "`) VALUES";
						}

						$sql_batch[floor($i / 100)] .= " ('" .
							implode("','", array_values($data[$i])) . "'),";

					}

					// Do our queries
					foreach($sql_batch as $sql) {

						// Trim off any final commas
						$sql = trim($sql, ",");

						// Execute our query
						$sql1 = $minidb->prepare($sql);
						$sql1->execute();
					}

					echo "<br>Import Complete.";
					//echo "<meta http-equiv=refresh content=2;URL=.>";
				}
				else{
					echo "Invalid file. Please Wait.";
					echo "<meta http-equiv=refresh content=1;URL=.>";
					/*echo "<script type='text/javascript'>alert('Please Check your File');</script>";*/
				}

IOFactory.php

    /**	PHPExcel root directory */
    if (!defined('PHPEXCEL_ROOT')) {
    	/**
    	 * @ignore
    	 */
    	define('PHPEXCEL_ROOT', dirname(__FILE__) . '/');
    	require(PHPEXCEL_ROOT . 'Autoloader.php');
    }

Autoloader.php

    class PHPExcel_Autoloader
    {
        /**
         * Register the Autoloader with SPL
         *
         */
        public static function Register() {
            if (function_exists('__autoload')) {
                //    Register any existing autoloader function with SPL, so we don't get any clashes
                spl_autoload_register('__autoload');
            }
            //    Register ourselves with SPL
            return spl_autoload_register(array('PHPExcel_Autoloader', 'Load'));
        }       //function Register();