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[samo]

OK so I batch add my files. I chmodd every folder to 777 and every picture file in each folder to 755. Tell me why only some pictures in some folders don't have preview thumbnails? I mean, I click on the 'red x boxed error' picture and it pops up with the picture perfectly. I can see it. It's just I don't see the thumbs. When I proceed to sort the files into a folder, the result pictures are blank too (a.k.a the 'red x boxed error' pics)

[Paver]

Are there any special characters in the offending filenames?  Are there differences in the sizes?  If you rename one of the files, does it upload correctly or not?

It's unlikely this is your problem, but here's an example of a file-specific problem that was never figured out, but was avoided with a work-around: http://forum.coppermine-gallery.net/index.php?topic=32049.0

Basically, you need to use troubleshooting steps to figure out what the differences are.  Use the scientific method (the basis of most good troubleshooting): fix everything and then vary one parameter - see what happens.  Repeat with other parameters.