deleting images in cart gives a "fatal error"

Have just been contacted by a client who is trying to order some images. They added the wrong image and when trying to delete the image in the cart it gives the following error message:
Fatal error: Cannot use string offset as an array in /home/anthonyd/public_html/blog/wp-content/plugins/image-store/_inc/cart.php on line 252

Any help would be appreciated.