have you downloaded any extra mods? or messed with the configs? if so its a mod conflict
It means you have an ugly stone world with a skeleton in the background and a square of red.
Hope that helps
LAN works with anything. you need to make sure you have the same mods, the same configs and the same modpack before you can play. LAN can sometimes not be found so if LAN isn't working try downloading Himachi and follow the tutorials on YouTube.
hope that helps