10 Gigabit Ethernet modules in Cisco 4500 series switches can operate in two modes. You can either “merge” two fiber optic ports into one 10 Gbit/s interface or use two separate interfaces, 1 Gbit/s each. However, in both cases you need to inform the switch in which mode should these modules operate – otherwise they won’t operate at all :)
You need to use the command:
hw-module slot slot_number port-group group_of_ports select [ tengigabitethernet | gigabitethernet ]
Update: the above is only true when using SFP modules for implementing fiber optic connections. With the new SFP+ modules, one module is enough to create a 10 Gbit/s link – there is no need to pair two modules in the configuration any more.