On Mac when my friend logs into tekkit lite it runs just fine.
When he installs some mods that I gave him (Forestry, Railcraft, Traincraft, Mo' Creatures, and Smart Moving) the game freezes after it gets to the main menu (singleplayer, multiplayer, etc).
I installed the exact same mods in the exact same way on my PC and the game runs perfectly.
I do not know why this wont work for him. Can somone give me some ideas?