Connection problems

Invalid Entity Data Item Type on Multiplayer Server

What it looks like in the log

java.lang.IllegalStateException: Invalid entity data item type for field 9 on entity class_1548['������'/<so>, l='ClientLevel', x=-<so>, y=<so>, z=-<s

How to fix it

  1. Join the server using the exact native Minecraft version it runs on rather than connecting through cross-version compatibility plugins like ViaVersion, ViaBackwards, or client-side ViaFabricPlus.
  2. Compare your installed mods with the server's mod list and remove any mods that add custom entity behaviors or data trackers if they are not installed on both sides.
  3. Test joining the server with an unmodded vanilla profile (or only pure rendering mods like Sodium) to confirm whether a client mod or a server-side plugin is causing the shifted entity data.
  4. If the error still happens on a vanilla client, send the log coordinates and entity ID from the error line to the server administrator so they can update their NPC, hologram, or protocol plugins (such as ProtocolLib or Citizens).
LoadersFabric, Quilt, Forge, Neoforge, Vanilla
SeverityBreaks something
CategoryConnection problems

Check your own log

Related errors

Connection problemsArchitectury & REI Server Packet Error: Cannot invoke class_8710$class_9154.comp_2242() because "type" is nullUpdate Roughly Enough Items (REI), Architectury API, and Fabric API to the latest available versions on both tConnection problemsFailed to bind to port — something is already using itAnother server copy is still running — stop itConnection problemsFailed to encode packet 'clientbound/minecraft:update_recipes' (Empty ItemStack not allowed)Open your client or server latest.log and search above the EncoderException for 'Couldn't load tag' or recipe Connection problemsMojang API Rate Limit: Too Many RequestsReduce the number of uncached custom player skulls placed in always-loaded spawn chunks so the server does notConnection problemsRead timed out / connection problems while downloadingThe launcher or loader could not reach the file serverConnection problemsSSLHandshakeException: PKIX Path Building Failed (Untrusted Certificate)Turn off local proxies, VPNs, or network accelerators (such as Watt Toolkit, Steam++, or Fiddler) and temporar