My first thoughts was a Word Template error, but when we tried from an old server, the remittances worked fine. We then tested a few other areas and received similar errors, which meant the problem is not template related.
The users had been logging on using published applications, so I logged onto the server directly and received the following error:
Microsoft Word isn't your default program for viewing and editing documents.
Do you want to select the files types that Word should open?
Just marking yes, isn't that easy as this is a Citrix XenApp server. However, I'm only involved as the Dynamics GP Consultant, so the issue was handed over to the Citrix team to investigate and resolve.