Guyz, same problem here.
I’ve FIXED this removing the BOM (byte order marker) from my wp-config.php and all my template files (i don’t know if template files really makes difference with this problem, but, you know 🙂 ), i was dealing with the BOM and whitespace at the top of pages and when i’ve finished the bom removing, the upload problem was gone.
Open your files (template files and wp-config.php) and re-save then in a simple editor, like Notepad, it will remove BOM.
Works for me 🙂
