Thanks for answering.
I tried putting thisform.cbserial_id.requery() to replace thisform.refresh to the codes. But the problem is still there.
In fact, I discovered that, even without the requery in the codes, after adding
record I can find the newly added record in the dropdown list of the combo box "cbserial_id", it was even placed in the correct order, which might mean
the combo box was refreshed OK. It probably wasn't the cause.
What keeps haunting me is the table order got messed up after the append action.
When prev button is pressed, the newly added record is always missing.
I am attaching the codes for the prev button. Thanks for helping.

Codes for prev button:
IF NOT BOF()
SKIP -1
THISFORM.refresh
ENDIF

>Try to use requery method for combo, instead of refresh after adding new record into table -source for combo
>>
>>5. Codes in my add record method:
>> APPEND BLANK
>> REPLACE serial_id WITH ALLTRIM(sNo)
>> THISFORM.refresh
>> WITH THISFORM.pageFrame1
>> .ActivePage = 2
>> .page2.txtremarks.SETFOCUS()
>> ENDWITH
>>