I checked this error log, but there only PHP notices, they can’t affect file uploading issue. Do you have situation, when files wasn’t uploaded after you enable debug log? If yes – can you give me log information for that time period.
I checked error log and found, that plugin “Email before download” generated fatal error. Probably there is conflict with this plugin (or maybe with some else).
Please try do disable this plugin and check, is this error is persist. If yes, please give me list of installed plugins on your site.