Been running Moi on my iMac (27" retina display) for almost two years now with no problems. Last time was about 3 weeks ago. Now this evening I launch the program and get a:

Unable to create Direct3D9 device.
Possibly an unsupported older video card, or hardware acceleration is disabled.
Check Control Panel / Display /Settings /Advanced / Troubleshoot

Message in the main window. I have not changed anything (that I am aware of) and the Mac OS has not had a "control panel" since OS 9 (well over a decade ago) and I don't see anything in the display preferences at the OS level that corresponds to a 2006 thread here int he discussions about "Unable to create Direct3D9 device." issues which discuss 32-bit color depth.

Anyone have an idea how I can fix this or even what to troubleshoot?

At this point MoI is suddenly non-functional as a result of this suddenly appearing issue.

As a follow-up and some more technical background info, here my Mac specs:

iMac (Retina 5K, 27-inch, Late 2014)
3.5 GHz Intel Core i5
8 GB 1600 MHz DDR3

Display: AMD Radeon R9 M290X
Type: GPU
Bus: PCIe
PCIe Lane Width: x16
VRAM (Total): 2 GB
ROM Revision: 113-C408A0-730
VBIOS Version: 113-C408A0-017
EFI Driver Version: 01.00.730
Metal: Supported, feature set macOS GPUFamily1 v3

Display Type: Built-In Retina LCD
Resolution: 5120 x 2880 Retina
Framebuffer Depth: 30-Bit Color (ARGB2101010)
Main Display: Yes
Mirror: Off
Online: Yes
Automatically Adjust Brightness: No

Ok, combing through an earlier thread, about MacOS X High Sierra:

http://moi3d.com/forum/lmessages.php?webtag=MOI&msg=8592.3

I followed the fix there and it seems to have done the trick. And now MoI is launching and running good as before.

Thank you Michael Gibson for posting that fix in that thread.

Hi Lestatdelc, yes it's a side effect of updating the OS, I'm glad you have it resolved now. I've also come out with a v3.2 release for the Mac version which has that setting needed to run on High Sierra changed by default. You can get the updated 3.2 version from here: http://moi3d.com/reinstall.htm

It also shouldn't be an issue with the v4 beta release which you can get here: http://moi3d.com/beta.htm - for v4 the Mac version has a lot of changes, it's a native compiled version now and doesn't use the "Wineskin" mechanism anymore. It is my hope that v4 will not be as sensitive to changes in new OS releases but we'll have to see. Wineskin is very sensitive.

- Michael

Thanks Michael.

I will check out the beta 4.

Is there a thread about what's new in the 4 version (particularly for us Macusers)..?

Hi Lestatdelc, there's a collection of the v4 beta release notes here:
http://moi3d.com/wiki/V4Beta

There's lots of things improved for the Mac version, like Retina support, 64-bit, full screen mode, trackpad navigation, ...

- Michael