You have a central server for DVA which is used by WebAccess for viewing file attachments or by any PO for QF Indexing. When a WebAccess user wants to preview and PPT attachment, it fails. However, any other attachment type succeeds with preview.
There was a bug fixed. If you had a DVA running locally on the WA server, then previewing PPT files worked fine. It was just a case when a DVA run on a remote, central server.
You will need to get a FTF build file 18.1.2-134495 or later. Also make sure there is java installed on the remote host.