Network Protocol Error (mod incompat?)

there IS a mod incompatibility (i think, anyways) but i have no idea what it is
can someone please tell me whats wrong and why i can't connect? my friends couldnt either and when they try to join, in console it just states and their userid etc etc lost connection: disconnected and doesnt send anything like an error message
heres a player log and heres the server log idk if they will help

Solution

it was polymer