Issue with top menu & "WP Lightbox" plugin

Hi, I use the "WP Lightbox 2" plugin for my images. But when I click on a picture, a drop-down menu appears just below the top menu and I don't know why ... I can't show you the url because my website is still offline (on local computer) but this is a screenshot : http://imageshack.us/photo/my-images/812/elwc.png/ (in red) Do you have an idea ? thanks ps : I use Catchbox 2.8.2