flat assembler version 1.71.39 (1048576 kilobytes memory)
D:\Program Files (x86)\Fasm\INCLUDE\api\Kernel32.inc [4]:
import kernel32,\
D:\Program Files (x86)\Fasm\INCLUDE\macro/import64.inc [50] import [24]:
label dq RVA _label
error: symbol already defined.

format PE64 console 
entry start 

include '%fasminc%\win64ax.inc' 

macro writeAndSort
{
        ; just place holder at the minute
        xor     rax, rax
}

macro calculate
{
        xor     rdx, rdx
        mov     rax, r12
        push    rax
        mul     rax     
        mov     rcx, rax                
        pop     rax
        shl     rax, 1
        mul     r13
        add     rcx, rax                
        mov     rax, r13
        mul     rax
        sub     rcx, rax                
        mov     [r14], r12
        mov     [r15], r13
        mov     [rbp], rcx
        add     r14, 8
        add     r15, 8
        add     rbp, 8
        dec     rbp
        jnz     @f
        call    WriteFile
    @@:
}

section '.text' code readable executable 

    start: 
        sub     rsp, 08
        mov     [sort], FALSE           
        mov     r12, 9999998            
        mov     r13, 1                  
        mov     rbx, 1000000            
        mov     r14, mList
        mov     r15, nList
        mov     rbp, highList
    .n6:
        calculate
        add     r13, 2
        cmp     r13, r12
        jb      .n6
    .m1:
        cmp     [sort], TRUE
        je      @f
        mov     [sort], TRUE            
        invoke  CreateFile, sortedmFile, GENERIC_WRITE, FILE_SHARE_READ, OPEN_ALWAYS, FILE_ATTRIBUTE_NORMAL, FILE_FLAG_SEQUENTIAL_SCAN, NULL
        mov     [sortedmHnd], rax
        mov     rdi, r12
        sub     rdi, mList
        invoke  WriteFile, [sortedmHnd], mList, rdi, bytesWritten, NULL
        invoke  CloseHandle, [sortedmHnd]
        invoke  CreateFile, sortednFile, GENERIC_WRITE, FILE_SHARE_READ, OPEN_ALWAYS, FILE_ATTRIBUTE_NORMAL, FILE_FLAG_SEQUENTIAL_SCAN, NULL
        mov     [sortednHnd], rax
        mov     rdi, r13
        sub     rdi, nList
        invoke  WriteFile, [sortednHnd], nList, rdi, bytesWritten, NULL
        invoke  CloseHandle, [sortednHnd]
        invoke  CreateFile, sortedhighFile, GENERIC_WRITE, FILE_SHARE_READ, OPEN_ALWAYS, FILE_ATTRIBUTE_NORMAL, FILE_FLAG_SEQUENTIAL_SCAN, NULL
        mov     [sortedhighHnd], rax
        mov     rdi, r12
        sub     rdi, highList
        invoke  WriteFile, [sortedhighHnd], mList, rdi, bytesWritten, NULL
        invoke  CloseHandle, [sortedhighHnd]
        mov     rbx, 1000000
        mov     r14, mList
        mov     r15, nList
        mov     rbp, highList
        jmp     .m12
    @@:
        writeAndSort
    .m12:
        inc     r12
        cmp     r12, [max_m]
        ja      .finished
        mov     r13, 2
    .n1:
        calculate
        add     r13, 2
        cmp     r13, r12
        ja      .m2
        calculate
        add     r13, 4
        cmp     r13, r12
        jb      .n1
    .m2:
        writeAndSort
        inc     r12
        cmp     r12, [max_m]
        ja      .finished
        mov     r13, 1
    .n2:
        calculate
        add     r13, 2
        cmp     r13, r12
        jb      .n2
    .m3:
        writeAndSort
        inc     r12
        cmp     r12, [max_m]
        ja      .finished
        mov     r13, 2
    .n3:
        calculate
        add     r13, 2
        cmp     r13, r12
        jb      .n3
    .m4:
        writeAndSort
        inc     r12
        cmp     r12, [max_m]
        ja      .finished
        mov     r13, 1
    .n4:
        calculate
        add     r13, 4
        cmp     r13, r12
        ja      .m5
        calculate
        add     r13, 2
        cmp     r13, r12
        jb      .n4
    .m5:
        writeAndSort
        inc     r12
        cmp     r12, [max_m]
        ja      .finished
        mov     r13, 2
    .n5:
        calculate
        add     r13, 2
        cmp     r13, r12
        jb      .n5
    .m6:
        writeAndSort
        inc     r12
        cmp     r12, [max_m]
        ja      .finished
        mov     r13, 1
        jmp     .n6

WriteFile:
        ret


    .finished:
        invoke  ExitProcess, 0

;************************************************************************************************** 
section '.data' data readable writeable 

align 8

        mFile           db "e:\m.dat", 00
        nFile           db "e:\n.dat", 00
        highFile        db "e:\high.dat", 00
        sortedmFile     db "e:\sortedmFile.dat", 00
        sortednFile     db "e:\sortednFile.dat", 00
        sortedhighFile  db "e:\sortedhighFile.dat", 00
        tmpFile         db "e:\tmp.dat", 00
align 8
        max_m           dq 3037000499
        sort            dq ?
        mHnd            dq ?
        nHnd            dq ?
        highHnd         dq ?
        sortedmHnd      dq ?
        sortednHnd      dq ?
        sortedhighHnd   dq ?
        tmpHnd          dq ?

        mList           dq 1000000 dup ?
        nList           dq 1000000 dup ?
        highList        dq 1000000 dup ?
        
;************************************************************************************************** 
section '.idata' import data readable writeable 

    library kernel32,'KERNEL32.DLL',\ 
            user32,  'USER32.DLL',\
            msvcrt,  'msvcrt.dll'

    include '%fasminc%\api\Kernel32.inc'  
    include '%fasminc%\api\User32.inc'  

    import msvcrt,\ 
            fopen,      'fopen',\ 
            fclose,     'fclose',\ 
            fwrite,     'fwrite',\
            fread,      'fread'

    

When you include win64ax you are already defining the imports. So when you place the imports again with "include '%fasminc%\api\Kernel32.inc'
" then you get an error for symbol already defined.

format PE64 console 
entry start 

include '%fasminc%\win64ax.inc' 

section '.text' code readable executable 

    start: 
code in here

section '.idata' import data readable writeable 

    library kernel32,'KERNEL32.DLL',\ 
            user32,  'USER32.DLL'

    include '%fasminc%\api\Kernel32.inc'  
    include '%fasminc%\api\User32.inc'  
    

Heh, okay that'll teach me to simply read and not test the code.

When all else fails, read the source