Module design:why design can't run in "virtex2"

[skywave]

I have some problems when I am running the modular design flow in Xilinx ISE 5.1i. After entering the top-level design codes and synthesizing them successfully, I enter commands like this"ngdbuild -p xc2v3000-bf957-6 -uc alu.ucf -modular initial alu.ngc alu.ngd", and I get a failed message"can't run ngdbuild in modular design mode for 'virtex2' architecture".I don't know why.