Just to let you all know I have solved my problem.
After having a little think I remembered A problem I had using Lightbox on a non ZC site.
my images were named correctly, andall had uploaded correctly, the problem was my LRG files were all saved with the jpg extension in uppercase, i.e. JPG. Making these all lowercase solved the problem. I remembere that the lightbox plugin dosen't like uppercase extensions.

Thanks for the help guys

Dan