Some Safari users are experiencing problems uploading files to WP. We are investigating a long-term fix to this issue. In the meantime, the following actions will correct the problem.
Clear cache and cookies for the amazonaws.com domain in Safari:
Preferences >> Privacy Tab >> Manage Website Data… >> search “amazonaws” >> select amazonaws.com and “Remove” button to clear it out) >> restart Safari
If you continue to be unable to upload files in Safari once the above is done, please contact our support center.