I see.   The authentication error message is not coming from "FlexStack Module". This is another scenario on C2960 Switches, but is similar troubleshooting and workaround: %ILET-1-AUTHENTICATION_FAIL: This Switch may not have been manufactured by Cis...

Hi, If this is the message: ILET-1-DEVICE_AUTHENTICATION_FAIL: The FlexStack Module inserted in this switch may not have been manufactured by Cisco or with Cisco's authorization...  You will need 15.2(6)E  instead of 15.2(4)E6.   FlexStack extended m...

hello there, Hard-reset/power-cycle the Switch(this is removing all cables from the Switch and connect them back), this procedure might need to be repeated two or three times. If authentication messages follow, let's open a case with us in TAC for re...