Shopping Cart Sessions - Think this is a simple prolem - hopefully

Evening all, I'm pretty stumped with this basic shopping cart I'm trying to integrate into my site, if u wanna see what I'm on about visit http://www.hostmaster-x.co.uk/Products.php. On my products script I've got the following: <?php $shoppingcart = array(); session_start(); session_register('shoppingcart'); if($buy != "") { $shoppingcart[] = $buy; //header("Location: $PHP_SELF"); /* echo "<B>Cart contains: <?=count($shoppingcart)?> items</B><BR><BR><BR>"; */ //exit(); } // Loads more code here ( code that works ) Of course I need a link so that I can buy a product, so I've got the following in a loop: echo "<a href=$PHP_SELF?buy=$i>Buy</a><BR>"; The link works fine for each product, the problem is that the ID of the product doesn't seem to be stored in the session and I get a whole pile of mysql errors which don't appear in the same page when products are displayed. The errors highlight the following code: while($ProductDetails = mysql_fetch_array($Q)) { $ProductID = $ProductDetails["ID"]; $ProductName = $ProductDetails["ProductName"]; $SellingPrice = $ProductDetails["SellingPrice"]; $ProductPicture = $ProductDetails["PictureOfProduct"]; $AmountInStock = $ProductDetails["AmountInStock"]; $Description = $ProductDetails["ProductDescription"]; $PictureOfProduct = $ProductDetails["PictureOfProduct"]; } if(mysql_num_rows($Q) > 0) Anyone got any ideas? I'm a bit lost as to why this doesn't work. G :) Public Sub House() On Error Resume drink If Pint.empty = True Then Pint.refill Else Pint.drink End if stomach.add Pint MsgBox " I've had .... " & stomach.count & " Pints" MsgBox "VERY DRUNK" End Sub