Something

<?php

//no error yet!
$error ="";

//get msg from POST
$boardMessage = $_POST['boardMessage']; 
$boardAgree = $_POST['boardAgree'];

//check message
if ($boardMessage == "")
	$error = "You did not enter a message!";
else
	$_SESSION['boardMessage'] = $boardMessage;
	
//check agree
if ($boardAgree == "")
	$error = "You did not agree to the Terms!";

 if($error != NULL){
	 $_SESSION['error']=$error;
	 header("Location: /Community+Board.html");
 }else{
	 header("Location: /Community+Board+Posted.html");
	 $_SESSION['boardMessage'] = "";
 }
                         
                         
?>