This advisory applies to the Enterprise Edition of MX-Contact:

All users need View, Add, Edit All and Delete All rights on all folders. (Keep in mind there is no data in the folders themselves, so giving a user Delete All permissions is no danger, but it is a requirement for MX-Contact.
Users do not need Owner permissions on a folder (which would allow them to delete the folder and/or modify the form associated with the folder) or Folder Contact rights.