I cannot target revision C of the Spartan-3A Starter Kit board. Why?
You can target revision D of the board without any issues.
This problem has been fixed in the latest EDK 9.2i Service Pack, available at:
http://www.xilinx.com/xlnx/xil_sw_updates_home.jsp
The first service pack containing the fix is EDK 9.2i Service Pack 1.