When the data required to serialize a networked object is larger than MTU, error messages are generated:

Channel {0} for connection {1} does not support fragmented messages; MTU: {1500}, message length: {1557}

Failed to send big message
UnityEngine.DebugLogHandler:Internal_Log(LogType, String, Object)
UnityEngine.DebugLogHandler:LogFormat(LogType, Object, String, Object[]) (at C:/Users/sean/uu/Runtime/Export/Logger/DebugLogHandler.cs:10)
UnityEngine.Logger:Log(LogType, Object) (at C:/Users/sean/uu/Runtime/Export/Logger/Logger.cs:42)
UnityEngine.Debug:LogError(Object)
UnityEngine.Networking.ChannelBuffer:SendBytes(Byte[], Int32) (at C:/Users/sean/uu/Extensions/Networking/Runtime/ChannelBuffer.cs:181)
UnityEngine.Networking.NetworkConnection:SendBytes(Byte[], Int32, Int32) (at C:/Users/sean/uu/Extensions/Networking/Runtime/NetworkConnection.cs:303)
UnityEngine.Networking.NetworkServer:SendBytesToReady(GameObject, Byte[], Int32, Int32) (at C:/Users/sean/uu/Extensions/Networking/Runtime/NetworkServer.cs:438)
UnityEngine.Networking.NetworkServer:SendWriterToReady(GameObject, NetworkWriter, Int32) (at C:/Users/sean/uu/Extensions/Networking/Runtime/NetworkServer.cs:409)