Full images not showing in NextGen Gallery

I’m using the NextGen Gallery plugin on the Portfolio page of my website at site.etccommunication.com. Rarely do the images, when clicked on, open to their full size. They stay “thumbnail square.” One image that’s opening properly is the Bridal Shower Invitation. One that isn’t opening properly is the Trade Association Newsletter. Can you give me any advice as to how to fix this problem? I’ve checked to make sure all the images are sized the same way and uploaded the same.

I’m willing to switch to a different gallery plugin, but I keep hearing this one’s the best.