In addition to marking the appropriate page/part security rights, be sure to mark the appropriate upload and manage rights within the document part itself. Follow the steps below to do so:
  1. Edit the documents part
  2. Click Add Users and Roles button under the Security Rights section
  3. Select the role/user
  4. Click Add > button
  5. Mark checkboxes for Upload and Manage appropriately
  6. Click OK
  7. Click Save