Library unit VPKG is not available in library UNISIM

I am trying to synthesize a code using ISE which contains a component fifo the fifo code is the following

-- synopsys translate_off library IEEE; use IEEE.STD_LOGIC_1164.ALL; library UNISIM; use UNISIM.VCOMPONENTS.ALL; use UNISIM.VPKG.ALL;

entity ifo is .................... .............. end ifo

ARCHITECTURE st of ifo is ......... ........ end st

-- synopsys translate_on

If I run the above code using ise it doesnt recognize the component at all. If I remove the line sysnopsys translate_off then it gives me following error Library unit VPKG is not available in library UNISIM

any ideas? Thanks

-D