I encountered this crash when trying to load Craftify in Forge using Sinytra Connector:

https://gist.github.com/Starexify/e726a19a1cdd4197b76c9dc14cb2f202

I reported to the Connector and the developer said this is a problem with the mod, it includes classes in a package that begins with java., which is prohibited by the JVM.

More here: Sinytra/Connector#959 (comment)

I just wanted to report this since more compatibility between mods is better.

Will be fixed when this gets merged EssentialGG/UniversalCraft#73

This has been fixed