Topic: How do I add pictures using Photoshop?

I created my photo gallery using the script provided for Photoshop, it worked fine...I was able to see my one test picture.  I added 4 more pictures to the input folder and reran the script, using the same input and output folder and I received this message from Photoshop...Error 1233: Expected a reference to an existing file/folder.  Now the gallery doesn't work.
I've deleted all of the files and reload them, and tried doing the process again, no luck! 
How can I fix this, and how do you properly add/change photos?