FM Client does not see file on FileMaker Cloud

[animation_master]

FileMaker Pro 15 Launch Center connects to our AWS instance with no problem. But then it reports

No files are currently hosted on AWS instancename.

Well, there ARE files currently hosted. We access them via WebDirect, so they must be hosted.
Moreover, when we launch a local copy of the file, FileMaker offers to open the remote copy with

This file has previously been uploaded to FileMaker Server. Use Hosted Version?

It even displays the proper address for the hosted file.
However Use Hosted Version returns this error:

The file “filename.fmp12“ could not be opened. (Extended privilege disabled)

So, we created a privilege set that extended privileges for fmwebdirect, fmapp and fmxdbc.
On the next launch of Remote Version, we got this:

FileMaker cannot share a file because FileMaker network sharing is turned off.

So, we turned on ODBC sharing, and on the next launch, we got this:

FileMaker cannot share files because another user is already sharing files using FileMaker Pro on this computer.

I’m going in circles here. Are these errors related? What am I doing wrong?

Edited April 16, 2017 by animation_master
Title was missing