Site CORE doesn't exist in the search path

Hello all,

I am importing my design from Encounter13 to Virtuoso (IC.5) in order to apply DRC and LVS checks by Calibre. But before 'streaming in' my design, I imported the LEF files. In icfb, when I do File->Import->LEF, I receive the following warning for every macro in the lef file.
Processing Macro '<cellname>'. *WARNING* Site CORE doesn't exist in search path. Ignored.
How can I get rid of this warning?

Detail info:
First I imported the LEF files, including the header (tech-lef file), then the body-lef file including the macro's info. In the header file I have the following info of the site core:
#------------------------------------------
# site definition for P&R
#------------------------------------------
SITE core
    SYMMETRY y ;
    CLASS CORE  ;
    SIZE 0.400 BY 3.200 ;
END core

In the body-lef file, every macro starts with the lines below:

MACRO <cellname>
    CLASS CORE ;
    FOREIGN <cellname> 0.000 0.000 ;
    ORIGIN 0.000 0.000 ;
    SIZE 2.400 BY 3.200 ;
    SYMMETRY x y   ;
    SITE core ;
    ....
    ....