I'm using Greyface patch 2.4 and it was working fineat first. I started a new game, still in New Sorpigal. Went to play today and it ran in a small window in the upper left corner. I used my mouse to expand the window and it worked, but still playing in a window. I edited the MM6.ini file to change borderless fullscreen from 1 to 0 but that did nothing. I didn't change anything else in the ini file or in game.

I had the same issue. MM6 was working in full screen initially. After restart, it changed to windowed mode permantently, I've reinstalled the game few times, tried F4 key, tried messing with ini file - nothing worked.

Then I've changed exe properties to "Windows XP compatibility" and "Run this program in 640x480" and it now works in full screen.

Yup same deal for me, was using the maximize window option but still in a window
Did anybody find a way to fix this besides setting the compatibility?

So I'll preface this by mentioning that I don't have this issue with my build, however 2 possible fixes do come to mind.

First, I have had issues in the past with other versions of Grayface's patch (MMVIII) with desktop resolutions over 1920x1080, now he did fix this in an update, but it may be worth trying the 1920x1080 desktop resolution if yours is higher natively.

Second, you could always try running MM6 with DGVoodoo2.
Be aware that you'll have to edit the mm6.ini with the following (SupportTrueColor has to be added in):

SupportTrueColor=0
BorderlessFullscreen=0

From what I gather from his MM6patch readme, the "SupportTrueColor" flag is what enables his custom engine, and will disable output through DGVoodoo2. It's also interesting that he notes that the flag will be disabled automatically in Windowed Mode. Which makes me wonder if it has anything to do with the issues you guys are having? Maybe also try setting it to "1" and running the game before trying DGVoodoo2....

If you haven't used DGVoodoo2 before, it's a program that is used to mimic old video cards in a current Windows Environment. Specifically for Glide and older DirectX games. Depending on if he's updated the program lately your web browser may say it's an unsafe site/program as it "hooks" onto your current DirectX to work (this is the reason behind the password on the zip file, anytime he updates Google doesn't like it until enough people tell them it's safe again). It is perfectly safe though, many people myself included have used it for years (Grayface even specifically mentions the DGVoodoo dll files in his readme).

On downloading DGVoodoo2 zip file you'll need the 3 main files installed into the MM6 folder, plus the 4 files in MS\x86 folder. Now run dgVoodooCpl.exe (Windows Defender will complain, run anyways) turn on "Inherit Color Profile in full screen mode" Don't play with "Output API" or "Adapters to use" as they can cause problems when changed from default settings.

Under the "DirectX" tab you can force anisotropic and anti aliasing if you'd like (I do). I did find with MM6 that forcing a higher resolution caused mouse issues, so I'd leave that at "unforced" at least initially. You can also uncheck the watermark if you'd like.

One final thing, I had to make sure my NVIDIA Control Panel's Scaling mode is set to "Aspect Ratio" with scaling performed by the "GPU" and "Override the scaling mode set by games and programs" is enabled to get the correct Aspect Ratio when using DGVoodoo2

Hopefully one of these fixes work for you!

Since applying Grayface Patch v.2.4 to M&M 6 & 7 and Grayface Patch v.2.4.1 to M&M 8 I have had to use:

"Run in 640x480 screen resolution" compatibility to achieve Fullscreen. I never had to do this before the v.2.4 (1) patches.

Not a big deal since it still gives you the same result as opening their respective .ini files and changing BorderlessFullscreen=1 to BorderlessFullscreen=0. (This only seems to work for M&M 6 now though.) At least for me.

I launched M&M 6 both ways and it looks exactly the same. M&M 7 & 8 crash after their intro movies if I use the "BorderlessFullscreen 1 to 0" fix. So I just use the "Run in 640x480" for all three now. I also use "Windows XP SP3" compatibility.

I'm running them on a Windows 7 64bit laptop.

Just free info.

I'm assuming you've tried hitting F4?