Devices will increment the “Inbound Unknown Protocols” error counters on interfaces if strange protocols are received. This is typically when network adapters receive IPX, AppleTalk, or Cisco Discovery Protocol (CDP) broadcasts from devices. These packets can be perceived as errors since they may be unwanted protocols on the network, or the network administrator may view these as valid packets that were successfully delivered although are of no use to the recipient device.

Go to the Config Tool -> Polling Tab:

Check the box "Ignore Unknown Protocols on Interfaces".