fastcraft-1.23.jar monitorBiomeDecorators = true
https://gist.github.com/354375b43fe362e9f48407d2ddd1aa94
and
https://gist.github.com/954593d2588517b9701ddf8703408373
what to do?

and was able to create a map, But then after 10 seconds crash.
https://gist.github.com/e6244a28cf38c1b42c161ca3e7df4532

UP
found the mod which causes crash
Farseek-1.0.11.jar
Streams-0.2.jar
on RTG-1.7.10-0.8.0-snapshot-5.jar all ok

A lot of other people have been reporting the 'Already Decorating' crash, so we'll look into this and try to get to the bottom of it.

Might also be related to the 1.23 version of Fastcraft because I haven't gotten this crash when testing RC-1 with Streams.

Other people who have posted crash reports:

CheshireKatt - http://pastebin.com/Pu102iYp

Titus_ - http://pastebin.com/MKyewZJr (line 514)

It's an odd error because it happen in a re-entrance of CPRTG.doGenerate(), and the code disallows that. The only thing I can think of is that something has made multiple copies of CPRTG.

Could it be the newer versions of Fastcraft? Two of the three crash reports are using Fastcraft 1.2.3 and the other is using 1.2.2

Decorating crash when loading game means I cannot get to stage to open a single world - at all, so cannot test this version. Note - using Fastcraft 1.21 still

RTG-1.7.10-0.8.0-RC-1
Streams-0.2
Farseek-1.0.11
Fastcraft 1.21

Time: 05/05/16 08:21
Description: Exception in server tick loop

java.lang.RuntimeException: Already decorating!!
at net.minecraft.world.biome.BiomeDecorator.func_150512_a(BiomeDecorator.java:97)
at net.minecraft.world.biome.BiomeGenBase.func_76728_a(BiomeGenBase.java:339)
at rtg.world.biome.realistic.RealisticBiomeBase.rDecorateSeedBiome(RealisticBiomeBase.java:295)
at rtg.world.biome.deco.DecoBaseBiomeDecorations.generate(DecoBaseBiomeDecorations.java:93)
at rtg.world.biome.realistic.RealisticBiomeBase.decorateInAnOrderlyFashion(RealisticBiomeBase.java:601)
at rtg.world.gen.ChunkProviderRTG.doPopulate(ChunkProviderRTG.java:1053)
at rtg.world.gen.ChunkProviderRTG.decorateIfOtherwiseSurrounded(ChunkProviderRTG.java:421)
at rtg.world.gen.ChunkProviderRTG$1.accept(ChunkProviderRTG.java:133)
at rtg.world.gen.ChunkProviderRTG$1.accept(ChunkProviderRTG.java:123)
at rtg.event.EventManagerRTG.onChunkLoadEvent(EventManagerRTG.java:272)
at cpw.mods.fml.common.eventhandler.ASMEventHandler_176_EventManagerRTG_onChunkLoadEvent_Load.invoke(.dynamic)
at cpw.mods.fml.common.eventhandler.ASMEventHandler.invoke(ASMEventHandler.java:54)
at cpw.mods.fml.common.eventhandler.EventBus.post(EventBus.java:140)
at net.minecraft.world.chunk.Chunk.func_76631_c(Chunk.java:923)
at net.minecraft.world.gen.ChunkProviderServer.originalLoadChunk(ChunkProviderServer.java:189)
at net.minecraft.world.gen.ChunkProviderServer.loadChunk(ChunkProviderServer.java:131)
at net.minecraft.world.gen.ChunkProviderServer.func_73158_c(ChunkProviderServer.java:101)
at net.minecraft.server.MinecraftServer.func_71222_d(MinecraftServer.java:265)
at net.minecraft.server.integrated.IntegratedServer.func_71247_a(IntegratedServer.java:130)
at net.minecraft.server.integrated.IntegratedServer.func_71197_b(IntegratedServer.java:153)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:387)
at net.minecraft.server.MinecraftServer$2.run(MinecraftServer.java:685)

My latest pull fixes the crash, although the Streams don't seem to be getting made. I'll have to talk to Delvr about this.

There's no problem with Fastcraft, this is happening because of Streams.

RTG-1.7.10-0.8.0-RC1
Fastcraft-1.23
Farseek-1.0.11
Streams-0.2
Seed: 6924026457310522769

This will crash on world init.

It will still crash if Fastcraft is removed.
It will stop crashing if Streams is removed.

Temporary fix added in 7704310 - will try to release another RC tonight so testing can resume whilst we investigate a solution for this.

I will not create a new question... could the problem be in something else.
sometimes if I find a thaumcraft biome in the log like this spam
https://gist.github.com/e74ec8deec8373ba28b4369230adef12
no crash
in Fastcraft has enabled this option for my tests
; Settings for debugging and workarounds
[debug]
; Specify whether FastCraft should monitor biome decorator invocations to try tracking issues with
; "Already decorating!!" exceptions down. This is only for investigating worldgen issues.
; Activating this will decrease world generation performance slightly.
; Valid values: true, false. default: false.
monitorBiomeDecorators = true

please tell me what could be wrong?
with the installed RTG was a spam too

The crash has been fixed but Streams don't generate at all in the current release. Delvr and I are working on this and we currently have the Streams generating but not correctly in unreleased test versions. They are done in a two-stage process and the second stage only gets done about half the time, leaving placeholder cobblestone where the Streams are supposed to go.

Fixed in 03f95eb