There is a difference between how the config DOUT is clocked with reference to CCLK between the Spartan-3 Generation and Spartan-II/-IIE.
The config DOUT is driven off the falling edge of CCLK for all Spartan-3 Generation devices. The Spartan-II/-IIE devices use the rising edge. When migrating a design from Spartan-II/-IIE to any Spartan-3 device, keep this difference in mind.
For more information on Spartan-3 configuration, please see the Spartan-3 Generation Configuration User Guide linked here: