PHP Coder to fix a sales tracking script

We have a software which is used to track sales from third-party websites. It is written in PHP and MySQL. There is a bug, any visitors from IE do not get tracked. The system works by firing a 1x1 pixel image from the third-party system and then checks the database to find a matching visitor on our end. At this point a sale is tracked. Please specify the following three words to be considered - fix fix fix. This works (as we believe) perfectly in Firefox, but not in IE. We are looking for a talented coder, preferably with experience in pixel tracking who can figure out this problem. Must be proficient in PHP, MySQL, DHTML, and CodeIgniter framework. The server uses FreeBSD.