Admin login - en lille fejl

Hej
Jeg har lavet et admin script, det består af 2 filer,
når jeg prøver at logge af for jeg fejlen:

Warning: Cannot send session cache limiter - headers already sent (output started at /var/www/hotels/1go/kingsize/html/admin-again/functions.php:14) in /var/www/hotels/1go/kingsize/html/admin-again/admin.php on line 20


Admin.php indeholder:
<?
    require( "functions.php" );
    session_start();
    if( isset( $action ) ):
        if( $action == "logout" ):
            session_unregister( "name" );
            session_unregister( "passwd" );
                  session_destroy();
            displayHeader( "Logout" );
            echo "
            <center><h4>Yeah, you're succesfully logged out !</h4></center>
            </body></html>";
        endif;
    endif;
    if( isset( $name ) && isset( $passwd ) ):
        if( $name != $adminName || $passwd != $adminPasswd || $name == "" || $passwd == "" ):
            error( "Nope, that's not it !" );
        elseif( !session_is_registered( "name" ) && !session_is_registered( "passwd" )
        && $name == $adminName && $passwd == $adminPasswd ):
            session_register( "name" );
            session_register( "passwd" );
            displayAdmin();
        elseif( session_is_registered( "name" ) && session_is_registered( "passwd" )
        && $name == $adminName && $passwd == $adminPasswd ):
            displayAdmin();
        else:
            error( "Hhmmm, something's wrong !" );
        endif;
    else:
        if($action != "logout"):
            displayForm();
            endif;
    endif;
   
    function displayForm()
    {
        displayHeader( "Login" );
        echo "
        <center><h4>Login in</h4></center>
        <div align=center>
          <center>
          <form method=post action=admin.php>
          <table border=0 cellpadding=0 cellspacing=0 width=230>
            <tr>
              <td width=70 height=20>User:</td>
              <td width=130 height=20><input type=text name=name size=20 maxlength=10></td>
            </tr>
            <tr>
              <td width=70 height=20>Password:</td>
              <td width=130 height=20><input type=password name=passwd size=20 maxlength=10></td>
            </tr>
            <tr>
              <td width=70 height=20></td>
              <td width=130 height=20><input type=submit value=\"  Login  \"></td>
            </tr>
          </table>
          </form>
          </center>
        </div>
        <p align=center><a href=java script:history.back()>Back</a></p>
        </body></html>";
    }
    function displayAdmin()
    {
        displayHeader( "Admin area" );
        echo "
        <center><h4>Admin Area</h4></center>
        <p align=center><a href=admin.php?action=logout>Logout</a></p>
        </body></html>";
    }
?>

functions.php indeholder:

<?
$adminName = "Webmaster";
$adminPasswd = "pass";

function displayHeader( $title )
{
    global $fontFamily, $fontSize, $visitedColor, $hoverColor, $linkColor, $forumTitle;
    echo "
    <html>
    <head>
    <title>$title</title>
    </head>
    <body>
    <center><h2>$forumTitle</h2></center>";
}

function error( $error )
{
    global $forumTitle;
    displayHeader( "Error Page" );
    echo "
    <center><b>&lt;Error Page&gt;</b></center>
    <center><h4><font color=#FF0000>$error</font></h4></center>
    <p align=center><a href=java script:history.back();>Back</a>
      </body></html>";
    exit;
}
?>