LBA Write Sector Problem

My write function writes one sector at a time without a problem, but when I create a loop to write multiple sectors a GPF will occur during random writes in the loop.... eg. one time it will write 5 sectors then GPF, next time 40 sectors then GPF, third time only 2 sectors then GPF, etc.

The difficult thing is that my read function is identical with the exception of command 20h, using EDI and INSW. When performing the same loop with read sector, it completes every time without error.

I've checked out some OS code that uses LBA writing in their file system, and it's pretty much the same as my code below, no signs of anything special that writing needs in which reading doesn't.

Does anyone know what I'm doing wrong? Is there perhaps some kind of controller reset I need to perform after each individual write? Thanks in advance!

Code:

;Write sectors 10,000 thru 10,100

 mov ebp,10000
rep_format:
    mov eax,ebp
 lea edi,[lba]
       stosd
       lea esi,[buffer]
    call hd_write_sector
        inc ebp
     cmp ebp,10100
       je looper
   jmp rep_format
looper:
       jmp looper




;Write Sector Function
hd_write_sector:
        cli
 push esi
    xor eax,eax
 mov dx,1F1h
 out dx,al
   mov dx,1F2h
 mov al,1
    out dx,al
   lea esi,[lba]
       lodsw
       inc dx
      out dx,al
           inc dx
      xchg al,ah
          out dx,al
           lodsw
       inc dx
      out dx,al
   xchg al,ah
          mov ah,0E0h
         add al,ah
           inc dx
      out dx,al
   inc dx
      mov al,30h
  out dx,al
waitwrite:
 in al,dx
    shl al,1
    jc waitwrite
        pop esi
     mov dx,1F0h
 mov ecx,100h
        cld
 rep outsw
   sti
 call hd_wait
        ret


;Hard Disk Wait Function
hd_wait:
     cli
 mov dx,1F7h
waitloop: 
       in al,dx
    cmp al,50h
  je waitok
   cmp al,0
    je waitok
        jmp waitloop
waitok:
    sti
 ret


;Variables and Buffers
lba dd 0
buffer times 512 db 24h