If you are using this widgets https://appstore.home.mendix.com/link/app/32/
It is not likely it will work on most recent version of Mendix, as the latest update was from 2014 (mx version 6) Many API’s have been changed since. If you have the skills; unzip the widget, which contains the source and upgrade the API use, https://apidocs.mendix.com/8/client/
Maybe before doing this validate if this widget works like you expect in a Mendix 6 version.
I sometimes find that clearing the browser cache resolves this.
Sorry I don’t have version 6 readily accessible to me … And I’m not familiar with API’s … Do I have another option? I basically am looking for a way to view attachments in an Explorer-like pane.