I keep getting this error. And I don't know why... Thanks
Notice: Undefined index: UserID in C:\wamp\www\tweetball\classes\word.class.php on line 35
<?php
session_start();
class Word
{
    private $m_sWord;
    private $m_sMessage;
    private $link;
    public function __set($p_sProperty, $p_vValue)
    {
        switch($p_sProperty)
        {
            case "Message":
                $this->m_sMessage = $p_vValue;
                break;
        }      
    }
    public function __get($p_sProperty)
    {
        $vResult = null;
        switch($p_sProperty)
        {
        case "Message": 
            $vResult = $this->m_sMessage;
            break;
        }
        return $vResult;
    }
    public function Save()
    {
        include("Connection.php");
        $sSql = "insert INTO words (word, FK_UserID) VALUES ('$_POST[message]','$_POST[UserID]')";  
        if ($rResult = mysqli_query($this->link, $sSql))
        {   
            echo "";
        }
        else
        {       
            throw new Exception('We could not save your word!');    
        }                   
        mysqli_close($this->link);
    }
    public function CreateNew()
        {
            $m_sHost = "localhost";
            $m_sUser = "root";
            $m_sPassword = "";
            $m_sDatabase = "tweetball";
                $link = mysqli_connect($m_sHost,$m_sUser,$m_sPassword,$m_sDatabase);
              if($link!=null){
                    $this->link=$link;
                }
                else
                {
                    throw new Exception("There seems to be a database problem. Try again later");
                }
    }
    public function getWord()
    {
            $m_sHost = "localhost";
            $m_sUser = "root";
            $m_sPassword = "";
            $m_sDatabase = "tweetball";
        $sSql = "select * from tweetball where WordID = 1;";    
        if ($rResult = mysqli_query($this->link, $sSql))
        {
            $singleRecord = mysqli_fetch_assoc($rResult);
            $message = $singleRecord['Word'];
        }
        else
        {       
            throw new Exception('We could get your word!'); 
        }                   
        mysqli_close($link);
        return($message);   
    }
}
?>
 
     
     
     
     
    