It's always possible cause of the problem could be Mojang or LearnToMod's server having problems or a firewall / antivirus being too overzealous. But usually when you see this error message, or "closed connection" or "Failed to connect to the server. Internal Exception: java.io.IOException: An existing connection was forcibly closed by the remote host" the problem is with your mods.
Some errors in your mods can prevent your mods from loading into your mod chest or overload your server world or Vox-l world.
Here's how to avoid this:
1. Always have one (but only one) function with the title main (lowercase) in each mod. The word 'main' is the signal that tells our software to begin running the mod.
2. Don't leave blocks floating around in white space, because that will create a parse error - if you like, you can right click and disable the blocks.
3. Don't leave blocks that have empty slots empty.
4. Just to be safe, don't let any function title have the title dosomething (this is the default title)
5. Don't loop something like 10000 times or summon a 5000 ender dragons or TNT. Start with small numbers, test the mod, then gradually increase the number.
First, downloading a new world from the LearnToMod homepage to reset your Minecraft world. If that doesn't work, try modifying your mods directly.
The quickest way to check the mods you've written is by clicking the 'Account' tab in the middle of the LearnToMod homepage. Scroll down and you'll see a list of your mods - don't forget to check badge mods, as well as mods you've designed yourself.
Clicking on the name of the mod will bring you to the editor screen, and from there, you can disable, delete or edit the blocks, or delete the entire mod (From the dropdown menu on the editor: delete)