Update 3.1.15 is compatible with WordPress 3.9.1 and includes the following changes:

• New Option: Disable WP-Filebse Stylesheet (wpfilebase.css)
• Users can upload to sub-categories even if they don’t have upload permissions for parent categories
• Fixed error `Unable to insert item into DB! Unknown column ‘cat_upload_permissions’ in ‘field list’`
• Fixed a bug in Dropbox sync when curl is not available