java.io.IOException: Can't serialize unregistered packet

[Nanabell]

Hello,

This is a re-post from the Github since I missed the fact that I was supposed to use this forum ?

I have found an already existing topic with this error and I would have tried the solution described but I don't have a 32bit java installed which I could uninstall.#

 

I've been hosting a very small server for a friend of mine and since yesterday we've been getting issues with the error

 

[19:19:00] [Server thread/INFO] [minecraft/NetHandlerPlayServer]: Nanabell_ lost connection: Internal Exception: io.netty.handler.codec.EncoderException: java.io.IOException: Can't serialize unregistered packet

 

So I started to investigate a bit, here is what I found out:

1. Rule out that it is a mod
   In the beginning, I was thinking it might be a mod which does some stuff it should not do. So I set up a completely fresh test instance with the only Forge installed.

2. The first connect always works
   Connecting for the first time to the Server does actually work without any issues. But any subsequent connection attempts will fail with the error above

3. Try with multiple Forge versions
   Originally this happened with Forge14.23.5.2808
   To rule out that it was an issue which was introduced recently I ran tests with:

• 14.23.5.2808: to see if it is fixed in the newest version
• 14.23.5.2768: to test with the recommended stable build
• 14.23.4.2703 to just test an old version

4. Checking Java versions
   I tried running Java & the Server with Java 8 update 181 and Java 8 update 201 both in the 64bit version
   I also have a Java 11 installed but I did not try it. (I did not remove it as a test yet though, since I need it for development on other projects, though if suggested that this might be the cause I will uninstall to see if it can fix it)

5. Does not happen with Vanilla 1.12.2
   Lastly, I just wanted to see if it was a Minecraft Server issue in general so I started a vanilla Server.
   And I was able to connect/reconnect with and without a modded client without any issues.

 

Hope you can use this info to figure something out. At this point, I am clueless to what to do other than to restart my server everytime one of us disconnects from the server.

 

sidenotes:
Minecraft: 1.12.2
Java: 1.8_181 & 1.8_201
Forge: 14.23.4.2703 / 14.23.5.2768 / 14.23.5.2808
OS: Windows 10 Pro (10.0.17763 Build 17763 (Windows Insider Build))
Server: was localhost'ed (happened on external connection as well though)

logs: debug.log

 

[Laike_Endaril]

I've also been getting this issue lately, and I *only* have 64-bit java 8 installed (jre 191 + jdk 191).  Started running into this when running single player from my mod dev environment, then opening to LAN and attempting to connect from MultiMC to test some multiplayer features.  This is a process I do quite commonly and normally don't have issues with.

 

I remember getting this error before, and I'm pretty sure I had found some way to prevent it, but now I can't remember how...I'll post here if I figure anything out.

[Laike_Endaril]

I noticed that if I run the client from MultiMC and open it to LAN, with all the same versioning of all the same mods / forge / mc, it works just fine.

And then, just for kicks, I tried deleting the build folder of my mod project.

 

Now it's working from my IDE as well.  It sounds like you're not running from an IDE though, so this probably won't help you.

 

Edit: And now it's not working again.  I'm not sure if deleting my build folder made it work on the next run, or if I just got lucky somehow.  I hate trying to debug this kind of issue.

Edited February 20, 2019 by Laike_Endaril