我用ISE调用modelsim 做布线布局后仿真出现如下错误：

# ** Error: (vsim-SDF-3261) netgen/map/top_map.sdf(4127): Failed to find matching specify module path.
# ** Error: (vsim-SDF-3445) Failed to parse SDF file "netgen/map/top_map.sdf".
# Time: 0 ps Iteration: 0 Region: /wav File: wav.tfw
# Error loading design
# Error: Error loading design
# Pausing macro execution
# MACRO ./wav.mdo PAUSED at line 9

究竟是怎么回事啊？大家帮帮我吧！

top_map.sdf第4127行（红色）代码如下：

(CELL (CELLTYPE "X_RAMB16")
(INSTANCE XLXI_4\/BU5)
(DELAY
(ABSOLUTE
(IOPATH CASCADEINA DOA[0] ( 405 )( 405 ))
(IOPATH CASCADEINB DOB[0] ( 405 )( 405 ))
(IOPATH CLKA DOA[0] ( 1647 )( 1647 ))
(IOPATH CLKB DOB[0] ( 1647 )( 1647 ))
)
)

型号是Virtex-4，为什么会出现这个错误？