Images download unreadable

Hi, when i download images from my server to my desktop i find when i try to open them that they are unreadable, Paint cant read them, no preview available...why is this? what setting can I adjust to fix works fine on my home computer, i down load no problem and can view the images but on my work computer no such luck and i cant for the life of me see what is different between the 2 versions of smartftp any help appreciated thanks mochi