My website does not load the enlarged image

I have a little problem with the additional images, that I am having trouble fixing.

I upload the first image through the admin into the main directory and name it testprod1.jpg (750x750 px) and it shows up correctly (screenshot #1)

If I click on that image it enlarges the image and properly using the lightbox (screenshot #2)

Then I create the second image, name it tesprod1_2.jpg (750x750 px) and upload it to the same directory as the original is. It also shows up in the product page correctly (Screenshot #3)

This is where the problems start
When I click on the additional image it starts loading the image, but never actually loads it (screenshot #4)

1 thing that I have noticed that the first image still loads and on the right bottom corner it says image 1 of 2 (screenshot #5)
but when i click next it does the same thing in screenshot #4

Does anyone have any ideas on what is causing this problem and how can it be fixed. Thanks

The fifth screenshot is attached to this post

UPDATE: While trying to fix this issue I installed Image Handler 4, and now even the main image that worked properly does not work anymore.

Another Update. The main images did not work because of a file name issue. When I hover over the main image the on bottom right of Google Chrome the link shows up as images/large/testprod1_LRG.jpg If this file exists, the larger image loads correctly, If it does not the error continues, however when i hover over an additional image the link looks like this
javascript:popupWindow('http://mydomain.com/index.php?main_page=popup_image_additional&pID=19&pic=0&products_image_large_additional=images%2Ftestprod1_2.jpg')