Thread:Project:Support desk/Image upload not working after upgrade/reply (6)

"The file you uploaded seems to be empty..." message indicate that the file hasn't arrived to MediaWiki.

This can be caused by wrong rewrite rules or weird mismatch in mod_alias (example: the wiki is configured at http://example.com but the server redirects you to http://www.example.com, the POST data is lost)

Another problem may be the temp directory configured in PHP for uploads (wrong permissions, etc), but I'm not sure if it would give some other error message.