"Different Network Format" error

Greetings, I have a player on my small Fabric server that is getting the following error message: "Steam 'n' Rails on the client uses a different network format than the server. You should use the same version of the mod on both sides." We have confirmed that my player is running the correct version of the mod for the correct loader and the correct version of Minecraft, even going so far as to send him the file ripped from the server itself. MC Version: 1.20.1 Fabric Loader: 0.5.010 Create Version: 0.5.1f Steam 'n' Rails Version: 1.6.3 I am able to connect to my server just fine, and we are all running the same mods both client and server side. Any insight would be appreciated.