library XilixCoreLib cannot be found

[ra]

Hi,
I'm trying to use a couple of packages from the XilixCoreLib. In my VHDL
file, I typed:

library XilinxCoreLib;
use work.iputils_conv.ALL;
use work.iputils_math.ALL;


If from the ISE Project Navigator I start modelsim, everything works.
However, If I try to synthetize, I get an error on the "library" line,
saying that library XilixCoreLib cannot be found. What should I do?

Note that before these lines I have

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_ARITH.ALL;
use IEEE.STD_LOGIC_UNSIGNED.ALL;

but I'm getting no error there.

Thanks,
RA