When SpongeForge is installed, Clients get a Internal Server Error when trying to join. This is what isee in the console:

[19:36:20] [Netty Epoll Server IO #1/INFO] [neid]: Patching class: "net.minecraft.network.play.server.SPacketBlockAction" with Transformer Group: "TransformerGroupBlockHardcoredConstants"
[19:36:23] [User Authenticator #1/INFO]: UUID of player D3nnis3n is 4995603c-ad89-46a1-b858-c8b3e8ba863d
[19:36:23] [Server thread/WARN] [Sponge]: No entity type is registered for class clayborn.universalremote.hooks.entity.HookedEntityPlayerMP
[19:36:23] [Netty Epoll Server IO #2/INFO] [FML]: Client protocol version 2
[19:36:23] [Netty Epoll Server IO #2/INFO] [FML]: Client attempting to join with 171 mods : levelup2@${version},[email protected],[email protected],[email protected],binniecore@unspecified,[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],vbe@GRADLE:VERSION-GRADLE:BUILD,[email protected],[email protected],architecturecraft@@Version@,[email protected],storagedrawersextra@@Version@,[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],mtlib@@Version@,[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],fastleafdecay@v14,[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],nei@${mod_version},[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],stevescarts@${version},[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],advancedrocketrycore@1,[email protected],[email protected],[email protected],[email protected],tinker_io@release 2.5.5e,[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],opencomputers|[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected]_for_1.12,[email protected],[email protected],[email protected],[email protected],[email protected],[email protected]
[19:36:23] [Netty Epoll Server IO #2/INFO] [FML]: Attempting connection with missing mods [spongeapi, sponge, dynmap, nucleus, pieconomy] at CLIENT
[19:36:29] [Server thread/INFO] [FML]: [Server thread] Server side modded connection established
[19:36:29] [Server thread/WARN]: Failed to handle packet for /178.27.85.65:61068
net.minecraft.util.ReportedException: Sending packet
at net.minecraft.network.NetHandlerPlayServer.func_147359_a(NetHandlerPlayServer.java:891) ~[pa.class:?]
at net.minecraft.server.management.PlayerList.handler$playerLoggedIn2$zim000(PlayerList.java:2011) ~[pl.class:?]
at net.minecraft.server.management.PlayerList.func_72377_c(PlayerList.java:367) ~[pl.class:?]
at net.minecraft.server.management.PlayerList.initializeConnectionToPlayer(PlayerList.java:1567) ~[pl.class:?]
at net.minecraftforge.fml.common.network.handshake.NetworkDispatcher.completeServerSideConnection(NetworkDispatcher.java:256) ~[NetworkDispatcher.class:?]
at net.minecraftforge.fml.common.network.handshake.NetworkDispatcher.access$100(NetworkDispatcher.java:72) ~[NetworkDispatcher.class:?]
at net.minecraftforge.fml.common.network.handshake.NetworkDispatcher$1.func_73660_a(NetworkDispatcher.java:205) ~[NetworkDispatcher$1.class:?]
at net.minecraft.network.NetworkManager.func_74428_b(NetworkManager.java:285) ~[gw.class:?]
at net.minecraft.network.NetworkSystem.func_151269_c(NetworkSystem.java:179) [oz.class:?]
at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:788) [MinecraftServer.class:?]
at net.minecraft.server.dedicated.DedicatedServer.func_71190_q(DedicatedServer.java:396) [nz.class:?]
at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:666) [MinecraftServer.class:?]
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:524) [MinecraftServer.class:?]
at java.lang.Thread.run(Thread.java:748) [?:1.8.0_131]
Caused by: java.lang.NullPointerException
at org.spongepowered.common.entity.player.tab.SpongeTabList.sendUpdate(SpongeTabList.java:190) ~[SpongeTabList.class:1.12.2-2503-7.0.0-BETA-2706]
at org.spongepowered.common.entity.player.tab.SpongeTabList.addEntry(SpongeTabList.java:161) ~[SpongeTabList.class:1.12.2-2503-7.0.0-BETA-2706]
at org.spongepowered.common.entity.player.tab.SpongeTabList.addEntry(SpongeTabList.java:141) ~[SpongeTabList.class:1.12.2-2503-7.0.0-BETA-2706]
at org.spongepowered.common.entity.player.tab.SpongeTabList.updateEntriesOnSend(SpongeTabList.java:205) ~[SpongeTabList.class:1.12.2-2503-7.0.0-BETA-2706]
at net.minecraft.network.NetHandlerPlayServer.rewritePacket(NetHandlerPlayServer.java:2560) ~[pa.class:?]
at net.minecraft.network.NetHandlerPlayServer.redirect$onSendPacket$zia000(NetHandlerPlayServer.java:2540) ~[pa.class:?]
at net.minecraft.network.NetHandlerPlayServer.func_147359_a(NetHandlerPlayServer.java:878) ~[pa.class:?]
... 13 more
[19:36:29] [Server thread/INFO]: D3nnis3n lost connection: Internal server error
[19:36:29] [Server thread/INFO]: D3nnis3n left the game

Hmmm... it seems SpongeForge can't handle the extended player class. Sad.

I'll need to come up with a compatibility patch. At this point I'm starting to wonder if writing a CoreMod for the hooks would be less prone to arcane errors...

What 1.12.2 spongeforge are you using? All the ones on the website and GitHub repro seem to crash on startup for me. They can't even initialize.

No it was the dedicated server that wouldn't start. I have used sponge on my own servers before. I will look futher into this when I can.

I believe you. It may be because of the debugger. If that is the case it will be very painful to try and fix. I definately want the mod to work with sponge if possible.

Reported fixed by D3nnis3n in 0.9.8! :)