If it is a 2012 R2, ensure the 2012 R2 Server has the update rollup for Windows RT 8.1, Windows 8.1, and Windows Server 2012 R2 that is dated November 2013.
Which includes a fix for KB2896636: You cannot use certain third-party devices to send a document to a shared folder in Windows RT 8.1, Windows 8.1, or Windows Server 2012 R2
Fault Code 016-781: Scan Server Connect Error
Simply means that the printer cannot connect to the ftp/smb, can you print to it from the server?
As you already said, it may or may not be supported by the OS.
Please remember to select "Accept as Solution" for posts that helped you solve the issue.
People in my company can no longer scan to our server from a 4595 up in their printer room. I've tried SMB and I've tried FTP. None of them work. We have a new server, a Windows Server 2012 box. I've been told by someone up there in Rochester that that could be a problem. I have no idea why. Something about the SMB for 2012 not matching the SMB on this very old printer.
I tried FTP, too. I can personally ftp to our server from my Mac or PC using the username and credentials that we use for scanning from the 4595. Using that username, I can ftp just fine to the server. But, it doesn't work from the 4595.
The error we get now is: 016-781.