use module within another module

I am trying to use merge_sort function that is contained in module-1 within  module-2.  No matter where I place the USE module-1 statement within module-2, I get compiler errors.  Either error #6285: There is no matching specific subroutine for this generic subroutine call. Or catastrophic error: **Internal compiler error: segmentation violation signal raised**.  Obviously I am missing something in my understanding of modules.

The basic set up is that module-1 is a merge sort module that sorts int64 arrays or arrays of objects of class face.  The second module is the face class and in its constructor I would like to call the int64 merge sort.

Here is a stripped down version of the merge sort module and the face module.  Error #6285 is thrown by the compiler when I place "use mergesort_class" at the top of module face_class; i.e. between lines 01 and 02.  The catastropic error is thrown by the compiler when instead I place the use mergesort_class at the top of function make_face; i.e. between lines 23 and 24.  See below the code snippets for the actual error messages.

I am relatively new to trying to use modules/classes in Fortran, so I am a bit shaky on the internal workings, despite lots of reading.  Any and all help will be greatly appreciated.

-sanjay

module mergesort_class   ! Source file mergesort_class
      implicit none

      private

      public :: mergesort

      interface mergesort
        module procedure ms_int64, ms_face
      end interface

      contains

      subroutine ms_int64(array,n,idx)
      implicit none

      integer          :: n
      integer          :: idx(*)
      integer (kind=8) :: array(*)

      ! relevant code to merge int64

      end subroutine ms_int64

      subroutine mergea_int64(array,l,m,r,idx)
      implicit none

      integer :: l,m,r
      integer :: idx(*)
      integer (kind=8) :: array(*)

      ! relevant code to merge int64

      end subroutine mergea_int64

      subroutine ms_face(array,n,idx)
      use face_class
      implicit none

      integer          :: n
      integer          :: idx(*)
      type(face)       :: array(*)

      ! relevant code to merge face objects

      end subroutine ms_face

      subroutine mergea_face(array,l,m,r,idx)
      use face_class
      implicit none

      integer :: l,m,r
      integer :: idx(*)
      type(face)  :: array(*)

      ! relevant code to merge face objects

      end subroutine mergea_face

      end module mergesort_class

      module face_class   ! Source file face_class.f
        implicit none
        private
        public :: face

        ! Type def for face
        type face
           integer (kind=8) :: hi,lo
           contains
             procedure       :: face_equal
             procedure       :: face_le
             generic, public :: operator (.eq.) => face_equal
             generic, public :: operator (.le.) => face_le
        end type face

        interface face
          module procedure make_face
        end interface face

        contains

        ! Constructor
        type(face) function make_face(a,b,c,d)
          implicit none
          integer, intent(in) :: a,b,c
          integer, optional, intent(in) :: d
          integer (kind=8)    :: n(4),m(4)

          ! relevant code to set up n( ) and m( )

          call mergesort(n,4,m)    ! Can not get this call to work

        end function make_face

        ! overloaded .eq.
        logical function face_equal(a,b)
           implicit none
           class(face), intent(in) :: a,b
           ! relevant code
        end function face_equal

        ! overloaded .le.
        logical function face_le(a,b)
           implicit none
           class(face), intent(in) :: a,b
           ! relevant code
        end function face_le


      end module face_class

ifort -c -O2 -Warn all -g -J/Users/sg/Feap/ver85/modules -I/Users/sg/Feap/ver85/include -I/Users/sg/Feap/ver85/modules -I/Users/sg/Feap/ver85/include/integer8 -I/sw/include face_class.f -o face_class.o
face_class.f(57): error #6285: There is no matching specific subroutine for this generic subroutine call.   [MERGESORT]
          call mergesort(n,4,m)
---------------^
compilation aborted for face_class.f (code 1)
make: *** [face_class.o] Error 1

ifort -c -O2 -Warn all -g -J/Users/sg/Feap/ver85/modules -I/Users/sg/Feap/ver85/include -I/Users/sg/Feap/ver85/modules -I/Users/sg/Feap/ver85/include/integer8 -I/sw/include face_class.f -o face_class.o
face_class.f: catastrophic error: **Internal compiler error: segmentation violation signal raised** Please report this error along with the circumstances in which it occurred in a Software Problem Report.  Note: File and line given may not be explicit cause of this error.
compilation aborted for face_class.f (code 1)
make: *** [face_class.o] Error 1