Problem declaration

Hello
My problem is that i want to create a file that contains some subroutine and call these
routines from an other files that contains the main program.
So in the main file i write this lines

NbMod   EQU 2
SRC     EQU 1000H
DST     EQU 1100H

PUBLIC  NbMod
PUBLIC  SRC
PUBLIC  DST

in the other file i write

EXTRN   Number(NbMod)
EXTRN   Number(SRC)
EXTRN   Number(DST)


                XSEG    AT Source       ; Error absolute expression required
SRC_RAM:        DS      16 * NbMod      ; Error Relocatable expression
                XSEG    AT DST          ; Error absolute expression required
DST_RAM:        DS      16 * NbMod      ; Error Relocatable expression

you can show the message error in the right of each line
but when i do these lines

NbMod   EQU 2
SRC     EQU 1000H
DST     EQU 1100H

in the same file ( i mean the file that contains the subroutine) i haven't this problem
i don't understand why since i declare the Public in the main and EXTRN in the subroutine files

Thank you