I just imported a world from Foundry and when I try to launch it I get this error.
Error starting Foundry: FVTT failed to launch world: The requested package by-moon-light is not available for use! Make sure your core software and game system are fully updated.
by moon light is the name of the world why is it calling for it like its a module?
Hi there 
Worlds, modules and systems are all technically packages so even a world failing to open will report a problem with loading it in this way.
It might be that the world’s system’s compatibility settings don’t allow it to start up on the configured Foundry server.
In this particular case, the Foundry server logs may tell us why the world is not available to launch on that particular configuration.
Have a look over here The Forge under View Foundry Logs and check to see if there’s an error message there that explains what’s going wrong.
If there’s nothing indicative there, please check your configured Foundry server version here The Forge (or here if you’re using Game Manager The Forge) and check the version of the system for your world you currently have installed.
Since it’s a new import, the versions might be different from your local Foundry version.