用iMPACT向xilinx芯片下载时出现这样的问题，有谁碰到过没有

RROR:iMPACT:499 - The bit file \'E:\\T6\\FPGA_DA\\da_form2.bit\' does not have the   startup clock set to \'JtagClk\'. Please re-generate the bitfile with the   startup clock option  set to \'JtagClk\'.好像是什么选项没有打开，不过我找了好久也没找到，那位仁兄遇到过？