Registration stopped working

Hi. We are using PunBB forum but i dont know what versions it is however our registration stopped working and i dont know what happend, it always say this.
* @contributor Mathias Michel */ // Constants to define return value of the Check() function. define("CHECK_OK", 0); define("CHECK_KO", 1); define("CHECK_MAX_TRIES", 2); // I set this like the KO, but it should be 3. I did that because I think // we don't need to know the difference (less cases to check in program) // For debug, you can set it to 3. define("CHECK_NO_SESSION", 1); class CaptchaBox { /** * how many attemps to grant the user to master the challenge * @access public */ var $maxTries = 3; /** * the background color of the generated image. Specified as a 3 element array for R, G and B values. Defaults to white. * @access public */ var $background; /** * the foreground color of the generated image. Specified as a 3 element array for R, G and B values. Defaults to dark blue. * @access public */ var $foreground; /** * the width of the generated image * @access private */ var $imageX = 0; /** * the height of the generated image * @access private */ var $imageY = 0; /** * the background color of the generated image after it has been allocated. Specified as an integer. * @access private */ var $bgAllocated; /** * the foreground color of the generated image after it has been allocated. Specified as an integer. * @access private */ var $fgAllocated; // all variables are private var $boxPosX; var $boxPosy; var $boxX = 20; var $boxY = 20; /** * Constructor of CaptchaBox. * Initializes foreground and background colors. * Initializes X & Y coordinates for image and box. * @access public */ function CaptchaBox() { $this->background = Array(255,255,255); $this->foreground = Array(0,0,128); $this->boxPosX = ($_SESSION["x"]?$_SESSION["x"]:null); $this->boxPosY = ($_SESSION["y"]?$_SESSION["y"]:null); $this->imageX = 200; $this->imageY = 150; } /** * Prepare the image the challenge is drawn on.* @access private * @return image a GDLib image resource */ function _createImage() { Header("Content-type: image/png"); if (function_exists("imagecreatetruecolor")) { $im = imagecreatetruecolor ($this->imageX, $this->imageY); } else { $im = imagecreate ($this->imageX, $this->imageY) or die ("Cannot Initialize new GD image stream"); } if (function_exists("imageantialias")) { imageantialias($im, true); } $this->bgAllocated = imagecolorallocate($im, rand(224,256), rand(224,256), rand(224,256)); $this->fgAllocated = imagecolorallocate($im, $this->foreground[0], $this->foreground[1], $this->foreground[2]); imagefill($im, 0, 0, $this->bgAllocated); return $im; } /** * Generate some random lines on the image. * @param image $im a GDLib image resource to modify * @param int $amount (optional) the number of lines to draw * @param char $direction the direction of the lines ('x'=horizontal, 'y'=vertical) * @access private */ function _generateImageNoise($im,$amount=5,$direction="y") { $x = imagesx($im); $y = imagesy($im); for ($i=0;$i<$amount;$i++) { $color = imagecolorallocate($im, rand(64,192), rand(64,192), rand(64,192)); if ($direction=="y") { $r1 = rand(0,$x); imageline($im, $r1, 0, $r1+rand(-5,5), $y, $color); } else { $r1 = rand(0,$y); imageline($im, 0, $r1, $x, $r1+rand(-5,5), $color); } } } function reset() { $_SESSION["x"] = null; $_SESSION["y"] = null; $this->boxPosX = null; $this->boxPosY = null; } function generateImage() { $_SESSION["x"] = rand(0,$this->imageX-$this->boxX); $_SESSION["y"] = rand(0,$this->imageY-$this->boxY); $text_color = 0; $im = $this->_createImage(); imagefilledrectangle($im, $_SESSION["x"], $_SESSION["y"], $_SESSION["x"]+$this->boxX, $_SESSION["y"]+$this->boxY, imagecolorallocate($im, 128+rand(-32,32), 128+rand(-32,32), 128+rand(-32,32))); $this->_generateImageNoise($im, $this->imageX/6, "x"); $this->_generateImageNoise($im, $this->imageY/6, "y"); imagepng($im); } function _doCheck() { return $_POST["x"]>=$_SESSION["x"] AND $_POST["x"]<=$_SESSION["x"]+$this->boxX AND $_POST["y"]>=$_SESSION["y"] AND $_POST["y"]<=$_SESSION["y"]+$this->boxY; } function check() { if ((session_id()=="") or !isset($_SESSION['captchabox']) or !isset($_SESSION["x"]) or ! isset($_SESSION["y"])) { return CHECK_NO_SESSION; // no session found, probably a bot }; if ($_SESSION["captchabox_tries"]>$this->maxTries) { return CHECK_MAX_TRIES; // max tries Reached } else { if ($_SESSION["captchabox_tries"]=="") { $_SESSION["captchabox_tries"] = 1; } else { $_SESSION["captchabox_tries"]++; } if($this->_doCheck()) { $_SESSION["captchabox_tries"] = 0; return CHECK_OK; // all is ok } else { if ($_SESSION["tries"]>$this->maxTries) { return CHECK_MAX_TRIES; //maxTries Reached } else { return CHECK_KO; } } } } } // class end ?>