@jahredi
It was a little while since I did it so I little fuzzy on it bit heres the process I think…
In NextGen Gallery options go to “Effects” tab and select “custom” for the JavaScript Thumbnail Effect. Then paste this into the box below – rel=”shadowbox[%GALLERY_NAME%]”
Then go to your “Manage Gallery” in Next Gen Gallery and select the gallery you are using for your slider. On the page showing all your gallery thumbnails in the 3rd column (“Alt&Title Text/Description”), in the single line field box (top of the 2 boxes) enter the full url to the normal size version of the image (https://www.youraddress.com/wp-content/gallery/gallery-title/image.jpg for example)
adjust your Shadowbox settings accordingly and it should work. A way to test is if shadowbox is activated the image should open in a lightbox kinda way. If Shadowbox is deactivated the image will open on a new page in the top left corner…well I have just checked it now and that is what happened when I deactivated SB.
As far as I remember I didnt make any adjustments to the carousel plugin files.
Hope that helps