nextgen-gallery cannot crop thumbnail

when i’m in “manage gallery” and I click on “edit thumb” from an image option a new dialogue box appears. great. however, when I try to click and drag to customize my thumbnail the box blinks black and nothing happens.

when I click “update” to see what will happen – i get the message “select with the mouse the area for the new thumbnail” – problem is, I can’t.

any ideas?

thanks!