Screen Exit - Table Control

I am trying to create a table control on screen SAPLXM06 (Screen exit for PO Header using exit MM06E005). I have a few issues. The first is that I can't use the table wizzard because, when it gets to the end, it says that it can't modify program SAPLXM06. So, I tried manually creating a table only I am not sure what I am missing.

I have a table control, called HAULTTABLE, on the screen. Then I have the following:

PROCESS BEFORE OUTPUT.
* MODULE STATUS_0101.
 loop AT IT_HAULTTABLE into wa_haulttable with control HAULTTABLE.

 endloop.
   module pbo.
*
PROCESS AFTER INPUT.
* MODULE USER_COMMAND_0101.
   loop at it_haulttable..
     module pai.
   endloop.

This passes the syntax check. However, when I go to ME23n and click on the "Customer Data" tab, I get an ABAP dump with the following:

CONTROL variable not found

The CONTROL "HAULTTABLE" was searched for but not found.

These is either an inconsistency between the screen and the program or

an incorrect ABAP statement (for example, REFRESH CONTROL .. FROM SCREEN

with incorrect control name).

What did I miss/what am I doing wrong?

Regards,

Davis