A little GD problem with batch add, important.

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When i select the directory of the pictures to add, it shows me the thumbnails of all the pics in the next step, all ok for the moment, but when i push in the next step, it shows me some picutres OK in blue color and others with the broken image, i click with right buttom in the broken image and  i choose show me the picture, and it appears ok and adds the pic to the galley but this is not normall, this is my problem, is a problem of my server, but how can i solve it? All the pictures will must be in blue and OK