The user gets DHCP through the user VLAN on the controller. Find out what user VLAN your SSID is tied to by typing "show ap essid" on the controller.
Next, you need to find out what port(s) that VLAN is connected to by typing "show vlan status".
If the DHCP server is not on the same VLAN as the user, you need to configure the controller with a helper address on that VLAN that forwards dhcp broadcasts to the DHCP server:
config t
interface vlan (vlan number of user vlan)
ip helper-address <ip address of dhcp server>
If the dhcp server and the users are on the DHCP VLAN, should just work.
Has this ever worked, or is this a new WLAN?