As an workaround you can hack this file:
./Dropbox/Dropbox/OAuth/Consumer/Curl.php
Modify default CURL options “$defaultOptions” following way
After string:
CURLOPT_FOLLOWLOCATION => false,
Add new string:
CURLOPT_SAFE_UPLOAD => false,
CURLOPT_SAFE_UPLOAD option was introduced in php5.5, and default was switched from false to true in php5.6, breaking the old way to upload files. Quick workaround is to set this option back to false as it was in php5.5
