I have encountered a problem where MAP fails if a timing-driven packing (-timing) is used in a design with DSP48 slices. The related error occurs:
"ERROR:LIT:382 - For DSP48 symbol
signal=Mmult__n0012_PCOUT471) attribute LEGACY_MODE is set to NONE. This does
not match with the OPMODE setting."
This problem has been fixed in ISE 7.1i SP3. For earlier revisions, this error can be avoided by setting the environment variable XIL_MAP_NO_DSP_AUTOREG or by not using -timing.
For general information about setting ISE environment variables, see (Xilinx Answer 11630).