When reconfiguring an access port to a trunk, the error shown in SW1's log indicates that there is a mismatch in the allowed VLANs on the trunk. To resolve this error, the allowed VLANs on both sides of the port-channel must be consistent. Option C is the correct command set because it specifies the allowed VLANs on the trunk to include VLANs 10 and 20, which must match on both switches to form a successful trunk link.