Whenever a turtle digs it attempts to call a method in net.minecraft.block.SoundType, which is only present in the client, therefore it crashes only when running the server separately.

Crash log:
java.lang.NoSuchMethodError: net.minecraft.block.SoundType.func_185845_c()Lnet/minecraft/util/SoundEvent; at dan200.computercraft.shared.turtle.upgrades.TurtleTool.dig(TurtleTool.java:285) at dan200.computercraft.shared.turtle.upgrades.TurtleTool.useTool(TurtleTool.java:126) at dan200.computercraft.shared.turtle.core.TurtleToolCommand.execute(TurtleToolCommand.java:36) at dan200.computercraft.shared.turtle.core.TurtleBrain.updateCommands(TurtleBrain.java:998) at dan200.computercraft.shared.turtle.core.TurtleBrain.update(TurtleBrain.java:185) at dan200.computercraft.shared.turtle.blocks.TileTurtle.func_73660_a(TileTurtle.java:259) at net.minecraft.world.World.func_72939_s(World.java:1802) at net.minecraft.world.WorldServer.func_72939_s(WorldServer.java:618) at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:709) at net.minecraft.server.dedicated.DedicatedServer.func_71190_q(DedicatedServer.java:387) at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:613) at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:471) at java.lang.Thread.run(Unknown Source)

I have temporarily solved the problem by dissasembling/assemblying TurtleTool.class and skipping the erroneous method call.

Oh, I see. I looked around and found nothing. I guess I have to look harder next time. Thanks for the coremod.

Don't worry. I just remembered this issue being reported before 😄.

Possibly the same as #122? If you're interested, I've put together a core mod which fixes some of the issues with 1.80pr0. As it is a core mod though, use with care.