Board Thread:Bug Reports/@comment-25782610-20150503222044/@comment-26172435-20151109144131

Yep, Same problem, but only in MPS. With or without mods. It occurs as soon as you set a personal waypoint. It happened to me and a friend of mine on the Steel Armies server today. The moment we pressed [Enter] to set a personal waypoint, the connection stopped and at relog, we get the above message. We both played with a modded client with similar package as mentioned above (all utilities like FastCraft, JourmeyMap, bspkrsCore, NEI, etc. and Conquest resourcepack). After restarting our client without any mods (except LOTR) and resourcepacks, we got the same result. Now we both can't relog on the Steel Armies server.

In single player this is not an issue!