This is a very weird and annoying problem. I got everything running smoothly on my Fedora desktop. However when I loaded WordPress on the production Ubuntu server (hardy) it crapped out. GD in installed and properly configured (with JPEG support and so on).
I took a look at the code. This problem occurs because function wp_get_attachment_metadata() returns a hash without ‘sizes’ key. And that hash is returned by a call to apply_filters(). From there is gets a bit murky and I’ve already spend more time on this then I should have. It would be nice if someone from the development team would take it from there.
