Images not uploading correctly

I am not sure what I’m doing wrong, but as I am loading new images into an existing gallery some of the new ones are not coming up, but others come out fine. Where the thumbnail should be, I just get this little link symbol link & the image will not pop up.

http://photozbycarolyn.com/?page_id=348

Hopefully it’s a simple fix, as I am not super knowledgeable when it comes to coding.

http://wordpress.org/plugins/nextgen-gallery/