I'm using the following code for my paging on my script

<?php
$pn = 0;


$result = mysql_query("SELECT * FROM tbl_product WHERE category = '$cat' ORDER BY id ASC ");

$nr = mysql_num_rows($result);
if (isset($_GET['pn'])) { // Get pn from URL vars if it is present
    $pn = $_GET['pn'];// filter everything but numbers for security(new)
} else { // If the pn URL variable is not present force it to be value of page number 1
    $pn = 1;
} 
//This is where we set how many database items to show on each page 
$itemsPerPage = 5; 
// Get the value of the last page in the pagination result set
$lastPage = ceil($nr / $itemsPerPage);
// Be sure URL variable $pn(page number) is no lower than page 1 and no higher than $lastpage
if ($pn < 1) { // If it is less than 1
    $pn = 1; // force if to be 1
} else if ($pn > $lastPage) { // if it is greater than $lastpage
    $pn = $lastPage; // force it to be $lastpage's value
} 

// This creates the numbers to click in between the next and back buttons
$centerPages = ""; // Initialize this variable
$sub1 = $pn - 1;
$sub2 = $pn - 2;
$add1 = $pn + 1;
$add2 = $pn + 2;
if ($pn == 1) {
    $centerPages .= '&nbsp; <span class="pagNumActive">' . $pn . '</span> &nbsp;';
    $centerPages .= '&nbsp; <a href="' . $_SERVER['PHP_SELF'] . '?pn=' . $add1 . '">' . $add1 . '</a> &nbsp;';
} else if ($pn == $lastPage) {
    $centerPages .= '&nbsp; <a href="' . $_SERVER['PHP_SELF'] . '?pn=' . $sub1 . '">' . $sub1 . '</a> &nbsp;';
    $centerPages .= '&nbsp; <span class="pagNumActive">' . $pn . '</span> &nbsp;';
} else if ($pn > 2 && $pn < ($lastPage - 1)) {
    $centerPages .= '&nbsp; <a href="' . $_SERVER['PHP_SELF'] . '?pn=' . $sub2 . '">' . $sub2 . '</a> &nbsp;';
    $centerPages .= '&nbsp; <a href="' . $_SERVER['PHP_SELF'] . '?pn=' . $sub1 . '">' . $sub1 . '</a> &nbsp;';
    $centerPages .= '&nbsp; <span class="pagNumActive">' . $pn . '</span> &nbsp;';
    $centerPages .= '&nbsp; <a href="' . $_SERVER['PHP_SELF'] . '?pn=' . $add1 . '">' . $add1 . '</a> &nbsp;';
    $centerPages .= '&nbsp; <a href="' . $_SERVER['PHP_SELF'] . '?pn=' . $add2 . '">' . $add2 . '</a> &nbsp;';
} else if ($pn > 1 && $pn < $lastPage) {
    $centerPages .= '&nbsp; <a href="' . $_SERVER['PHP_SELF'] . '?pn=' . $sub1 . '">' . $sub1 . '</a> &nbsp;';
    $centerPages .= '&nbsp; <span class="pagNumActive">' . $pn . '</span> &nbsp;';
    $centerPages .= '&nbsp; <a href="' . $_SERVER['PHP_SELF'] . '?pn=' . $add1 . '">' . $add1 . '</a> &nbsp;';
}
// This line sets the "LIMIT" range... the 2 values we place to choose a range of rows from database in our query
$limit = 'LIMIT '.($pn - 1) * $itemsPerPage .','.$itemsPerPage; //returns negative range
// Now we are going to run the same query as above but this time add $limit onto the end of the SQL syntax
// $sql2 is what we will use to fuel our while loop statement below


$result2 = mysql_query("SELECT * FROM tbl_product WHERE category = '$cat' ORDER BY id ASC $limit");//query fails
if(!$result2)
echo  "ERROR".mysql_error();

//PAGINATION DISPLAY

$paginationDisplay = ""; // Initialize the pagination output variable
// This code runs only if the last page variable is not equal to 1, if it is only 1 page we require no paginated links to display
if ($lastPage != "1"){
    // This shows the user what page they are on, and the total number of pages
    $paginationDisplay .= 'Page <strong>' . $pn . '</strong> of ' . $lastPage. '';
    // If we are not on page 1 we can place the Back button
    if ($pn != 1) {
        $previous = $pn - 1;
        $paginationDisplay .=  '&nbsp;  <a href="' . $_SERVER['PHP_SELF'] . '?pn='.$previous.'"> Back</a> ';
    } 
    // Lay in the clickable numbers display here between the Back and Next links
    $paginationDisplay .= '<span class="paginationNumbers">' . $centerPages . '</span>';
    // If we are not on the very last page we can place the Next button
    if ($pn != $lastPage) {
        $nextPage = $pn + 1;
        $paginationDisplay .=  '&nbsp;  <a href="' . $_SERVER['PHP_SELF'] . '?pn='.$nextPage.'"> Next</a> ';
    } 
}

?>
<!-- SOME HTML STUFF -->

THEN I USE THIS LOOP TO RETRIEVE ITEMS IN THE HTML BODY

<?php
while($row = mysql_fetch_row($result2)){
        echo '<div class="product_info">';
          echo '<div class="category_product_number">#'.$row[0].'('.$row[1].')'.'</div>';
         echo '<div class="category_product_description">'.$row[2].'</div>';
         echo '<div class="category_product_price">'.$row[4].'TL</div>';
      echo '</div>';
      }

      ?>

AND TO DISPLAY THE PAGINATION I DO THIS SOMEWHERE BELOW THIS LOOP
<div class="central_container"><span class="current_page">Showing <?php echo $paginationDisplay; ?></span></div>

HOWEVER, when i run the code, i get this error: "You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '-5,5' at line 1".

It seems i get a negative page number when i click the "NEXT" link or try to move to a new page (by clicking that page number), so the query returns a negative range for LIMIT. But I don't know why because i have a conditon that makes sure there are no negative page numbers. I know it's a lot of code but any help figuring out the issue will be appreciated. Thanks

Well this is some weird shit indeed, there does not seem to be anything wrong with your code. Have you tried echo-ing $limit? E.g.:

echo $limit;

And see what it is? Is it really -5,5? If yes, you could try echo-ing $pn each time its value changes, to see where it goes wrong.