Can't access admin - blank page

Tried uploading backup copy of shop after installing B1G1 free module, which didn't work. Store "front" is appearing but I can't get in the back end. Any help appreciated, willing to pay "pro" to fix it. Thank you.

Get this error, which in WordPress I know what it means!: HTTP Error 500 (Internal Server Error): An unexpected condition was encountered while the server was attempting to fulfill the request.

What does the Error Log say?
(ftp to the stores directory on your webserver then goto cache and open the myDEBUG-adm file with the highest number (will be the last in the directory theoretically)

this is why it is showing blank, and depending on what it says changes the fix

It says:

[13-Sep-2011 07:48:20] PHP Fatal error: Cannot redeclare zen_update_products_price_sorter() (previously declared in /home/sprinks/public_html/shop/zc_admin/includes/functions/general.php:2680) in /home/sprinks/public_html/shop/zc_admin/includes/functions/functions_prices.php on line 1334

But have no clue how to fix it.

And this is line 1325 to 1334:

// set the products_price_sorter
  function zen_update_products_price_sorter($product_id) {
    global $db;

    $products_price_sorter = zen_get_products_actual_price($product_id);

    $db->Execute("update " . TABLE_PRODUCTS . " set
                  products_price_sorter='" . zen_db_prepare_input($products_price_sorter) . "'
                  where products_id='" . (int)$product_id . "'");
  }