Installed Apr 29 build, and ran Max 2016.
Now, in Max 2016 I have changed the default folder (apparently, I forget!), as the default path in the RTT is now pointing at a folder on my F: drive, so a completely unrelated location.
Interestingly, leaving this as the default and rendering from RTT fails to create the file. If I manually change it to another path, it works and creates the file - even if I change it to the sceneassets/images location that wasn't working before.
So it seems specifically to do with the default path only, and seems to occur in 2016 in the same way as 2017?
Hope this helps!
Tom