it crashed when loading a world with the official caves and cliffs preview datapack

and after that i launched again opened thw world and closed after that i quited the game

and than i launched mc again and than it crashed again

my save file https://www.dropbox.com/s/gcq682h2s7bdyo8/21w15a%20with%20OFFICIAL%20datapack.zip?dl=0

my newer crash log 

Minecraft Crash Report -------- Minecraft Crash Report ----// Surprise! Haha. Well, this is awkward.
Time: 14-4-21 20:34Description: Unexpected error
java.lang.IllegalStateException: Missing: ResourceKey[minecraft:worldgen/biome / minecraft:plains] at gr.d(SourceFile:405) at ehy.a(SourceFile:543) at bwa.b(SourceFile:67) at bwy.a(SourceFile:50) at ehy.a(SourceFile:565) at ehy$$Lambda$5577/1417153932.fetch(Unknown Source) at net.minecraft.util.CubicSampler.a(SourceFile:40) at ehy.a(SourceFile:565) at elt.a(SourceFile:88) at elz.a(SourceFile:1127) at elu.a(SourceFile:953) at elu.a(SourceFile:771) at dun.e(SourceFile:1073) at dun.e(SourceFile:700) at net.minecraft.client.main.Main.main(SourceFile:217)

A detailed walkthrough of the error, its code path and all known details is as follows:---------------------------------------------------------------------------------------
– Head --Thread: Render threadStacktrace: at gr.d(SourceFile:405) at ehy.a(SourceFile:543) at bwa.b(SourceFile:67) at bwy.a(SourceFile:50) at ehy.a(SourceFile:565) at ehy$$Lambda$5577/1417153932.fetch(Unknown Source) at net.minecraft.util.CubicSampler.a(SourceFile:40) at ehy.a(SourceFile:565) at elt.a(SourceFile:88) at elz.a(SourceFile:1127) at elu.a(SourceFile:953)
– Affected level --Details: All players: 1 total; [ekw['jarn123'/122, l='ClientLevel', x=572.58, y=84.90, z=532.95]] Chunk stats: 841, 0 Level dimension: minecraft:overworld Level spawn location: World: (192,63,-256), Section: (at 0,15,0 in 12,3,-16; chunk contains blocks 192,-64,-256 to 207,319,-241), Region: (0,-1; contains chunks 0,-32 to 31,-1, blocks 0,-64,-512 to 511,319,-1) Level time: 39085 game time, 26892 day time Server brand: vanilla Server type: Integrated singleplayer serverStacktrace: at ehy.a(SourceFile:370) at dun.c(SourceFile:2259) at dun.e(SourceFile:724) at net.minecraft.client.main.Main.main(SourceFile:217)
– System Details --Details: Minecraft Version: 21w15a Minecraft Version ID: 21w15a Operating System: Windows 7 (amd64) version 6.1 Java Version: 1.8.0_51, Oracle Corporation Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation Memory: 579766000 bytes (552 MB) / 2147483648 bytes (2048 MB) up to 2147483648 bytes (2048 MB) CPUs: 8 JVM Flags: 9 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xss1M -Xmx2G -XX:+UnlockExperimentalVMOptions -XX:+UseG1GC -XX:G1NewSizePercent=20 -XX:G1ReservePercent=20 -XX:MaxGCPauseMillis=50 -XX:G1HeapRegionSize=32M Launched Version: 21w15a Backend library: LWJGL version 3.2.2 build 10 Backend API: ATI Radeon HD 5400 Series GL version 3.2.13417 Core Profile Forward-Compatible Context 15.301.1901.0, ATI Technologies Inc. GL Caps: Using framebuffer using OpenGL 3.2 Using VBOs: Yes Is Modded: Probably not. Jar signature remains and client brand is untouched. Type: Client (map_client.txt) Graphics mode: fancy Resource Packs: vanilla Current Language: English (US) CPU: 8x I

can't reproduce

My world says I cant load it because "Loading of worlds with extended height is disabled"

it says loading of world with extended height is disabled because 
"World height has been switched back to the 1.16 levels
......
Worlds created in snapshot 21w05b or any earlier version can now once again be opened
Worlds created in any version between snapshot 21w06a and 21w14a can no longer be opened"
from https://www.minecraft.net/en-us/article/minecraft-snapshot-21w15a

worked for me

Thank you for your report!
We're tracking this issue in MC-197616, so this ticket is being resolved and linked as a duplicate.

If you would like to add a vote and any extra information to the main ticket it would be appreciated.

If you haven't already, you might like to make use of the search feature to see if the issue has already been mentioned.

Quick Links:
📓 Bug Tracker Guidelines – 💬 Community Support – 📧 Mojang Support
📓 Project Summary – ✍️ Feedback and Suggestions – 📖 Game Wiki
_{-- I am a bot. This action was performed automatically! Please report any issues on Discord or Reddit}