Well, recently ive installed flans planes mod on my server which I only
run with 2 friends on it as well as me. Its been running without a
problem until one of us tried to teleport. The server just becomes
incredibly laggy for a few seconds, and then crashes, with this error
shown in my server log:

java.lang.NoSuchFieldError: aU

at ly.a(Unknown Source)

at net.minecraft.server.MinecraftServer.b(Unknown Source)

at net.minecraft.server.MinecraftServer.h(Unknown Source)

at net.minecraft.server.MinecraftServer.run(Unknown Source)

at bo.run(SourceFile:422)

Any advice on how to fix this, as this is kinda game breaking for us...

Thanks in advance,
Luke