Error: multiple products blocks the screen

hi, when you add about 20 products to shopping cart a window starts coming down from the top and covers the screen. this is obviously wrong and need fixing.

this can also be seen on your demo page, see a screenshot below when 22 products added. the more you add, the bigger this window gets and makes the site unusable.

your quick assistance is much appreciated as this is causing some problems on a live site.

thanks

J! 1.5.2.3
VM 1.1.9

sorry, screenshot wasn't attached corrrectly, trying again.