Describe the crash
User and friends playing on 2.77.3 server. They kept disconnecting with an error saying that an entity equipment packet was larger than expected. The user wasn't sure what the cause might be and didn't have any relevant information. However, looking at the log, it seems that there may have been an issue breaking a block that drops xp (like coal) potentially with a special modded piece of equipment (or even a vanilla tool modified in some way). Information is super scarce, but in case you see something like this again, figured it might be useful.

Crash Log
https://pastebin.com/Zcg7qJXg

Info (please complete the following information):

• Modpack Version: 2.77.3
• Server or Singleplayer: Server
• Version the world was created on: ?

Additional context
https://www.minecraftforge.net/forum/topic/65101-error-during-attempt-to-join-server/ This looks similar? A reinstall might fix it