Link to paypal contains incorrectly formatted item amount

Created by: rowjamesrow

Hi, have a site on Drupal 7.18, CiviCRM 4.2.7, and cloned the latest Cividiscount module from here, but when I apply a discount to an event I'm setting up, the link that gets sent to Paypal "contains an incorrectly formatted item amount". I removed the discount and it works. Any idea why this might be occuring?