This is a common error that occurs when the user is trying to run a 'stale' book. Meaning, the book is in the user's inventory, but the mod's code isn't on the server. And/or the user is missing a main()function. That's a necessary entry/starting point for the mod. When the user runs the mod book, our server is told to look for a main() function.

 Here are some thing you can do to reload the code:


- First ensure you are connected; if you're connected, on the main homepage you'll see 'server status: online' 

- Press the mod button for that mod. Look for the yellow text in Minecraft that states "mod loaded (mod_name)"

- Try making a small, meaningless edit to the code, such as a variable assignment. Then press the mod button again.

- ** Make sure your mod has a main function in its code

- Make sure the word main is in all lowercase letters

- Try downloading a smaller-sized Minecraft world from the LearnToMod homepage.

If you've tried those things and it's still not working, let support know at