Follow this template except for feature requests. Use pastebin when providing /protocol dump and any relevant errors.

java.lang.reflect.InaccessibleObjectException: Unable to make protected final java.lang.Class java.lang.ClassLoader.defineClass(java.lang.String,byte[],int,int) throws java.lang.ClassFormatError accessible: module java.base does not "opens java.lang" to unnamed module @725bd9a8
at java.base/java.lang.reflect.AccessibleObject.checkCanSetAccessible(AccessibleObject.java:357)
at java.base/java.lang.reflect.AccessibleObject.checkCanSetAccessible(AccessibleObject.java:297)
at java.base/java.lang.reflect.Method.checkCanSetAccessible(Method.java:199)
at java.base/java.lang.reflect.Method.setAccessible(Method.java:193)
at com.comphenix.protocol.reflect.compiler.StructureCompiler.generateClass(StructureCompiler.java:299)
at com.comphenix.protocol.reflect.compiler.StructureCompiler.compile(StructureCompiler.java:213)
at com.comphenix.protocol.reflect.compiler.BackgroundCompiler$2.call(BackgroundCompiler.java:204)
at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1130)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:630)
at java.base/java.lang.Thread.run(Thread.java:831)
Dump:
Parameters:
com.comphenix.protocol.reflect.StructureModifier@72f54ba0[
targetType=class net.minecraft.server.v1_16_R3.PacketHandshakingInSetProtocol
target=
converter=
fieldType=class java.lang.Object
data=[private int net.minecraft.server.v1_16_R3.PacketHandshakingInSetProtocol.a, public java.lang.String net.minecraft.server.v1_16_R3.PacketHandshakingInSetProtocol.hostname, public int net.minecraft.server.v1_16_R3.PacketHandshakingInSetProtocol.port, private net.minecraft.server.v1_16_R3.EnumProtocol net.minecraft.server.v1_16_R3.PacketHandshakingInSetProtocol.d]
defaultFields={public java.lang.String net.minecraft.server.v1_16_R3.PacketHandshakingInSetProtocol.hostname=1, private net.minecraft.server.v1_16_R3.EnumProtocol net.minecraft.server.v1_16_R3.PacketHandshakingInSetProtocol.d=3}
subtypeCache={}
customConvertHandling=false
useStructureCompiler=true
]
manager:
com.comphenix.protocol.injector.PacketFilterManager@3d4ac1d8[
unhookTask=com.comphenix.protocol.injector.DelayedSingleTask@4ef14e6b
packetListeners=[PacketAdapter[plugin=HolographicDisplays, sending=ListeningWhitelist[priority=NORMAL, packets=[REL_ENTITY_MOVE_LOOK[class=PacketPlayOutRelEntityMoveLook, id=40], SPAWN_ENTITY_LIVING[class=PacketPlayOutSpawnEntityLiving, id=2], SPAWN_ENTITY[class=PacketPlayOutSpawnEntity, id=0], REL_ENTITY_MOVE[class=PacketPlayOutRelEntityMove, id=39], ENTITY_METADATA[class=PacketPlayOutEntityMetadata, id=68]], gamephase=PLAYING, options=[]], receiving=EMPTY_WHITELIST], PacketAdapter[plugin=ServerListPlus, sending=ListeningWhitelist[priority=NORMAL, packets=[OUT_SERVER_INFO[class=PacketStatusOutServerInfo, id=0], SET_PROTOCOL[class=PacketHandshakingInSetProtocol, id=0]], gamephase=PLAYING, options=[ASYNC]], receiving=ListeningWhitelist[priority=NORMAL, packets=[OUT_SERVER_INFO[class=PacketStatusOutServerInfo, id=0], SET_PROTOCOL[class=PacketHandshakingInSetProtocol, id=0]], gamephase=PLAYING, options=[ASYNC]]]]
packetInjector=com.comphenix.protocol.injector.netty.ProtocolInjector$5@47dc2a6c
playerInjection=com.comphenix.protocol.injector.netty.ProtocolInjector$4@1f2cd17c
inputBufferedPackets=[]
recievedListeners=com.comphenix.protocol.injector.SortedPacketListenerList@74838740
sendingListeners=com.comphenix.protocol.injector.SortedPacketListenerList@30c51dad
hasClosed=false
classLoader=PluginClassLoader{plugin=ProtocolLib v4.6.0, pluginEnabled=true, url=plugins\ProtocolLib.jar}
reporter=com.comphenix.protocol.ProtocolLib$1@166cce93
server=CraftServer{serverName=Paper,serverVersion=git-Paper-756,minecraftVersion=1.16.5}
library=ProtocolLib v4.6.0
asyncFilterManager=com.comphenix.protocol.async.AsyncFilterManager@6f324a13
knowsServerPackets=true
knowsClientPackets=true
phaseLoginCount=2
phasePlayingCount=3
packetCreation=false
nettyInjector=com.comphenix.protocol.injector.netty.ProtocolInjector@1224c40f
pluginVerifier=com.comphenix.protocol.injector.PluginVerifier@e121590
hasRecycleDistance=true
minecraftVersion=(MC: 1.16.5)
debug=false
]
Sender:
com.comphenix.protocol.reflect.compiler.BackgroundCompiler@867e3d0[
listeners={com.comphenix.protocol.reflect.compiler.StructureCompiler$StructureKey@3b63ff60=[com.comphenix.protocol.injector.StructureCache$1@3ca13154]}
listenerLock=java.lang.Object@8118e73
compiler=com.comphenix.protocol.reflect.compiler.StructureCompiler@16b1b474
enabled=false
shuttingDown=false
executor=java.util.concurrent.Executors$FinalizableDelegatedExecutorService@217fbc11
reporter=com.comphenix.protocol.ProtocolLib$1@166cce93
unknownPermGenBean=java.lang.Object@146102fb
permGenBean=
disablePermGenFraction=0.65
]
Version:
ProtocolLib v4.6.0
Java Version:
16.0.1
Server:
git-Paper-756 (MC: 1.16.5)

Make sure you've done the following:

• You're using the latest build for your server version
• This isn't an issue caused by another plugin
• You've checked for duplicate issues
• You didn't use /reload

Debug paste link:

Description and relevant errors:

Duplicate of #1162

This issue was resolved in build 499+.