I am running Weaver 2010 theme on 3.0.4 with no mods and when I use the "Custom Background" option under "Appearance", I can select a file from my computer and click "upload", but I'm immediately presented with a blank white screen--nothing on it. I tried to view the page source for errors, but the page source is completely empty on that screen. If I hit the "back" button in my browser and try again, same result. This happens no matter what size image I try to upload.
This has happened on every version of wordpress I have had for this particular site since Custom Background became available on 3.0. Also note, even though I am getting a white screen, it appears the images are being uploaded... just to the wpcontent/uploads folder (default for Media). So... I'm at a loss for how to fix this. My other 4 wordpress sites work with the custom background just beautifully. This site is on a different server. I manually updated to 3.0.4 tonight and it did not fix this problem.