On one switch i have etherchannel: mode on, on other there is no etherchannel configuration. How switches detects misconfiguration and put porth in errordisabled state ?
I am not completely sure (and I don't have the equipment by me right now) but I believe that the EtherChannel Misconfig Guard checks the misconfiguration by the fact that in an Etherchannel, only a single port should transmit and receive BPDUs. Therefore, if a set ports is not bundled in an Etherchannel, each of them will eventually transmit BPDUs. This fact will be recognized on the other switch and the entire port channel will be moved to disabled state.