I dont see how that could happen at line 572, but at line 569, you have the following code:
<textarea name="SpecialInstruction" cols="40" rows="1"><?php echo $_SESSION['SpecialInstruction']; ?></textarea>
change that to:
<textarea name="SpecialInstruction" cols="40" rows="1"><?php echo isset($_SESSION['SpecialInstruction'])?$_SESSION['SpecialInstruction']:""; ?></textarea>