A case has been seen where a Map Fatal Error occurs when "trim unconnected logic" in map option is unchecked (equivalent to adding -u option in map command).
General Description: FATAL_ERROR:x4kma:x4kmacarry.c:1134:220.127.116.11 - COUT0 signal still exists on CY4 CLB: U1/fifo16/dramfifo_dual_ram_fifo/even_placement_read_counter/newSim41/cy4. The G-LUT is already in use. Process will terminate. Please call Xilinx support.
The workaround for the above error is check "trim unconnected logic" in map option. This problem is fixed in the A1.5/F1.5 release.