Why is my FFT not being generated for Virtex-II, when using ISE 6.1i?
This is because the XCO has an extra "2" after the XilinxFamily specification.
The work-around is to manually generate the Cores and place them in your directory:
1. Generate the ISE Project Navigator project.
2. Modify the XCO files in the "./corework" directory:
SET XilinxFamily = Virtex2
3. Regenerate the Cores using CORE Generator.
4. Move the ".edn" files to the implementation directory to replace the incorrectly generated cores.
5. Copy the cores to the "./corework" directory
6. Uncheck the Generate Core option in SysGen, for each of the DA FIR cores.