Unlike the other Cisco 7900 series IP phones, the Cisco 7935 IP conference phone does not have a 10/100 port to connect to a PC. Therefore, the concept of voice or auxiliary VLAN is not directly applicable. This can cause problems.
To resolve this problem, remove all references to voice VLAN or auxiliary VLAN from the port on the switch to which the Cisco 7935 IP conference phone connects. Put that port in the VLAN whose number corresponds with that of the voice VLAN.
For Cisco Catalyst 2900XL and 3500XL series switches, this is a sample configuration for the port: