I have an issue after upgrading to WP 3.5 that I could not resolve following what seemed to help others.
Uploading any but very small images generates a statement "HTTP error" in the upload screen. The uploaded image is visible in the media library, and I can click on 'edit', but when I then want to e.g. resize or otherwise manipulate it, it says that there is no image data and I should re-upload.
- Same issue in different browsers
- Memory size is 256M
- Disabling all Plugins didn't help
- Running Twenty-Twelve Theme didn't help
- WP_DEBUG does not return any hints
- even 900px width images, 150KB don't upload. A smaller 45KB image uploaded successfully
- I have tons of free space on the server