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I had the same problem last night after upgrading from 2.5 to 2.6...
the thumbnails were showing in the Random Picture Block, but when u went to the album home page, the thumbnails weren't showing in the latest listings and the submit and description were jumbled up.. When u went to the categories, the thumb nails appeared as normal, but when u clicked 1 to view it full size the image disappeared.. Right clicking on the Red X that appeared and choosing properties produced the line that the path to the image was in correct altho the correct path was there ie. modules/myalbum/photos/ but that's all it shown where's the correct path was modules/myalbum/photos/25.jpg you see the filename was missing..
i dunno why this happened, But doing what the previous posts mentioned and removing all the template files for the album 1 by 1 and then exiting and then re generating the template list.. Solved the problem 100%..
Maybe the programmer could look into that slight bug on upgrading for future users.