I'm having this exact same problem with a 2.5 installation. Using GD2. Tried to upload an image, was given the following error, and then boom, blank page.
Unable to move file [/tmp/phphsZjl7] [/home/httpd/vhosts/astroclassifieds.com/httpdocs/classifieds/data//18/TOA150-EM400.jpg]
I see the double / in the url and went into the admin settings to fix that, but I'm still getting a blank page. Do I need to try flushing something? The code fix above is not present in 2.5.