Perhaps your screen set has some LUA 5.2 (4300) code that is not compatible with LUA 5.3 (4612)? Although I can't say this is exactly the issue, I can say it is most likely the issue. You can start commenting out custom code in 4300, block by block if needed, until the screen loads in 4612. That way you can determine what is causing the problem. Then we can help you updating your LUA code.
Both builds can coexist on your PC at the same time. Just install 4612 into another directory, say "C:\Mach4Hobby-4612"
Steve