With DFFS 4.102, if you have any rule on an edit form that makes a field readonly, that rule will also set Attachments to readonly and remove the Attach Files from the Action bar Ribbon. Having the impact that you will not be able to add attachments if you have rule that sets any field to readonly.
This was not the case with DFFS 4.0 so it was introduced somewhere between 4.0 and 4.102