if you are fishing using the fishing rod and something such as a sudden crash and you login again it will crash the world/server as soon as you log in. it is very repeatable. happens with and without mcpc+. here is a pastebin of the crashlog http://paste.ubuntu.com/6627044/ and the forgemodloader-0 paste: http://paste.ubuntu.com/6627057/
Also you have to have the bobber still out in the water when the sudden shutdown happens in order for this to happen. Only way to fix it that I have found is to go in with world edit and delete the bobber that is in the water