When I create a new gallery and add new images, it gets stuck with processing images after two or three images.
It sounds like JuiceboxBuilder-Lite is choking on a certain image (or images).
If you try to add a batch of images more than once, does JuiceboxBuilder-Lite stop processing then images on the same image number each time?
Here are a few things to check and try which should hopefully point you in the right direction.
(1) Try adding your images in small batches to try to find a specific image that JuiceboxBuilder-Lite fails to successfully process. You may have one or more images that are somehow corrupt (perhaps just even corrupt metadata could prevent JuiceboxBuilder-Lite from successfully processing images).
(2) If you find an image that causes the problem, then try resaving it in an imaging program (such as Adobe Photoshop) to see if this resolves the problem.
(3) Also, if you find a problematic image (or have a small batch of images that consistently fails), please zip the image(s), upload the file somewhere and provide a download link so that I can try to replicate the problem with the same images that you are using.
(4) Try creating a fresh gallery with a completely different image source (maybe a different camera or phone or perhaps just some sample images from the internet) to see if the problem still occurs.
These suggestions might not solve your problem but they should at least help to narrow down possible causes.