I've installed the new DW CC 2017, and the latest Extension Manager, started DW a few times, restarted, re-installed but CC 2017 is not available in the Extension Manager, it closes after the message 'There was no Dreamweaver detected'.
I am working on OSX, version 10.12.1

Hello Dik,
Please do this:
Open Finder and press Shift-Cmd-G. Type ~/Library/Application Support in the dialog box, and click Go. You should then be able to find the configuration folder for Dreamweaver CC2017 at the following location:

Adobe/Dreamweaver CC2017/

Please tell me what do you see in it?

Hello Theodor,

I see 3 directories:

cloudpref
en_US
nl_NL

That is the issue then.
You have two language folders there and there must be only one.

In one of them (en_US or nl_NL) there is no version.xml file in the Configuration folder.

So please check which of the two folders miss the Configuration\version.xml file: en_US or nl_NL and remove it. This will fix the issue you are having.

Removed the 'en_US' folder. Problem fixed, thanx.