Sorry, there is nothing we can do about this. The Windows OS itself has a limit of 10,000 graphics objects per process, and the editor needs at least one icon per object not including everything else a typical Windows app needs, which is probably pushing you over the limit. Addressing this would require fundamentally rearchitecting the editor. This work is being done for C3, but it is too late for C2. I am shocked that anyone would ever run in to this limit anyway, since that is a truly extraordinary number of images to be using. All you can do is try to reduce the number of images used, or one other workaround is to export your project every time you want to test it, which applies spritesheeting and reduces the number of images.
Ashley
Hmm... In Windows 10, when I run preview on Chrome - It still not working like in Windows 7: 90% of loading and "stop".
But: preview working in Microsoft Edge... 5000 objects, 6000, 8000 - I don't know how, but it works