Implementing Cisco IP Switched Networks (SWITCH v2-0) (#26)

After an EtherChannel is configured between two Cisco switches, interface port channel 1 is in the down/down state. Switch A is configured with channel-group 1 mode active, while Switch B is configured with channel-group 1 mode desirable. Why is the EtherChannel bundle not working?

The switches are using mismatched EtherChannel negotiation modes.
The switch ports are not configured in trunking mode.
LACP priority must be configured on both switches.
The channel group identifier must be different for Switch A and Switch B.