I am currently setting up a server, but run into this problem every time I try to interact (place and use, but not destroy) with various blocks added by mods inside the game. These include, but are not limited to: Lucky Blocks, Chest (Battle Towers) and chests added by Iron Chests. The Server crashes instantly and I get following crash report (taken from fml): java.lang.NoClassDefFoundError: net/minecraft/client/Minecraft (Full Log: https://pastebin.com/9FRpSqX9)
There appear to be errors with the following mods, from what I can understand: TooManyItems, ChocolateQuest (Better Dungeons), Metroid3Cubed, MoreSwords, Tree Capitator and Twilight Forest. All are PlayerInteractEvent errors.
Also, Dungeons by BetterDungeons are not generated.