Hello there, I also posted this in another topic feathuring a different but similar problem (because I guess internally related). But I guess I'm not the only one it ever happened to. So I'm just putting this here because this error will have a specific topic, and people can post their own solution. DISCLAIMER It worked for me : I'm not assuming it can work for everyone. And be wary of not deleting any system font....or you'll get a beautiful not loading windows black screen. Hence, I'm posting that solution here as a possible mean to an end. You can jump to the second point directly, I'll just be explaining the backstory. 1 - My problem : It occured after a fresh install on W10, and installing all my fonts manually in the "Windows/fonts" folder. opening a project with custom fonts. When trying to change the font file used for one of the created font, GMS gave me an error before I could even do anything, just by entering the dialog box. It could not find the font. As in "does not exist" font. Yet, opening the windows font folder, IT DID exist, and yes, I had installed it (and many more). Scrolling down the menu, there was actually NO TRACE WHATSOEVER of any of the fonts I had installed before hand, right after my fresh W10 install. I figured "Might as well try a font manager to see if there's a problem" and went for NexusFont. First time I used that software. And....SURPRISE it could not find any of my font as well !!! 2 - On to said method. Let's delete them all one by one ! Went down the scrolling menu, it was the exact same thing as the list from NexusFont for my font folder contents. Went to said folder, and first, I copied all the fonts not showing in a new folder on my desktop (can be anywhere else, doesn't matter). Then I manually deleted all these fonts from the windows/font folder. !!!!!! DO NOT DELETE ANY SYSTEM FONT !!!!!! I open NexusFont back, and after a quick search on the internet, figured out how to install fonts. Just right click on "Sample group" --> "Add Folder". Select the folder where you put your custom fonts. Once in the list, Ctrl+A to select them all, right click ---> "INSTALL" in the windows/font folder. I did a Windows restart here for good measure. Back into GMS after the restart......and voila, it worked. 3 - Conclusion I'm not sure if I will ever encouter the same problem. Hope not. And I used NexusFont only for this problem, I'm not trying to advertise any soft, I don't use it (even if I can figure it has its use for people working with fonts or for writing puroposes). I hope it solved your problem.