ExternalObject not loading on Windows

Hi all,

Weird issue...   I've built an ExternalObject library for Windows and Mac to be loaded from InDesign ExtendScript.   It's using the curl library to do some https access from a remote server.

Anyway, works great on MY machine in Windows and Mac.  I can't get it to load on other machines in Mac.    Even with ExternalObject.log = true, all it says is "ExtObj: load error!".

I've tried several versions of ID, all the way back to ID 6, and CC2015.  (Works on all of the above on my PC).

My PC is Windows 10 32bit running on a VM on my Mac.   Other machines I've tried this on have been a Windows 10 PC (64 bit), and on another Mac VM Windows 10 32 bit.

My first suspicion is that there is a missing DLL dependency.  I've used dumpbin to review the dependent DLL's and they all seem to be present.  I wrote a stub program that loads the DLL library and calls a function and that functions on all platforms - so it's able to load the DLL and dependencies that way - just not via ID.

I've built the DLL using Visual Studio 2015 community edition.

I'm quickly running out of ideas on other things to check....