Dynamic title tags and Google

[system]

Hi All.

I added dynamic title tags to my website at: http://www.farmstockforsale.co.za/

Specifically pages like these:
http://www.farmstockforsale.co.za/fulldetails-Huge_Plough_Groot_Ploeg_For_Sale_Te_Koop-23.html
http://www.farmstockforsale.co.za/fulldetails-Mix_Breed_of_Chickens_For_Sale-12.html
http://www.farmstockforsale.co.za/fulldetails-Old_Farm_Cheap_Tank_Tanker_Truck_For_Sale-31.html

You will see that the landing page(fulldetails) is the same for each, but the title for each is not.

Google finally started indexing these pages and now says that I have duplicate tags?
This is part of the code:
[php]
session_start();
include(“db/configure.php”);
include(“db/database.php”);
include(“db/constants.php”);
include(“functions.php”);

$url = $_SERVER["REQUEST_URI"];
$pos = strpos($url, "-");

if($pos !== false)
{
	$title = substr($url, strpos($url, "-")+1);
	$title = substr($title, 0, strpos($title, "-"));
	$title = str_replace("_", " ", $title);
}

[/php]

<title><?php echo $title; ?></title>

Any idea what I am doing wrong?