[Unanswered] Mapping error

when I place my block that i made i get the error java runtime error block.crystalcut does not have mapping this is a bug!!! nothing else

I'm not to sure about it because you have no error log.

Will see if I can send it but it's on the start client thing so I can't really do it I will see if I can tupe it up tommorow

well I dont get an error log either it dosn't crash just when I re enter the world the block and anything I placed that touched it was gone

here is the error

Code:

java.lang.RuntimeException: class net.minecraft.src.TileEntitycomp is missing a mapping! This is a bug!
at net.minecraft.src.TileEntity.writeToNBT(TileEntity.java:49)
at net.minecraft.src.TileEntitycomp.writeToNBT(TileEntitycomp.java94
at net.minecraft.src.ChunkLoader.storeChunkInCompound(ChunkLoader.java:176
at net.minecraft.src.McRegionChunkLoader.saveChunk(McRegionChuckLoader.java:66)
at net.minecraft.src.ChunkProvider.saveChunks(ChunkProvider.java:132)
at net.minecraft.src.ChunkProvider.saveChunks(ChunkProvider.java:168)
at net.minecraft.src.World.func_650_a(World.java:315)
at net.minecraft.src.GuiIngameMenu.drawScreen(GuiIngameMenu.java:80)
at net.minecraft.src.EntityRenderer.updateCameraAndRender(EntityRenderer.java:710)
at net.minecraft.src.EntityRendererProxy.updateCameraAndRender(EntityRendererProxy.java:23)
at net.minecraft.src.client.Minecraft.run(Minecraft.java:517)
at java.lang.Thread.run(Thread.java:662)

I typed that out so there might be typos how do I copy from command promt and can someone try to give me a fix