[Plugin: NextGEN Gallery] cannot show caption under thumbnail

Hi, I am using WordPress 3.0.5 with Weaver 2 theme. I want to show image captions under thumbnails. What I do is to just write [nggallery id=4 template=caption] into a new page, to show the images belonging to the gallery with id = 4. My gallery preferences is to show 10 images in a page, win a total of 5 columns; this setting best fits my page width by the way. Thumbnail size is 88×116 pixels for each image, which is the one-third of each image size. So nothing seems wrong in the image listing but captions are not shown under the thumbnail..What should I do? thanks in advance.