Is ".isc" file generation support for Virtex-4 devices included in ISE 9.1i?
The ".isc" file generation support was turned off in 9.1i and 9.1i SP1.
This problem has been fixed in the latest 9.1i Service Pack available at:
http://www.xilinx.com/xlnx/xil_sw_updates_home.jsp
The first service pack containing the fix is 9.1i Service Pack 2.