As Namoi also mention, use a "safe select" which means that you never change the grid's recordsource. In your form's init:

SELECT cusno,cusname FROM cusmas  where .F. INTO CURSOR cusmas_srh readwrite && create an empty cursor to drive the grid
Index on cusno tag cusno

This will replace ALL the code you showed:

SELECT cusno,cusname FROM cusmas  INTO CURSOR curtemp readwrite && A temp cursor
SELECT cusmas_srh && Which drives the grid
ZAP
Append from dbf('curtemp')
GO top
Use in curtemp && Not really necessary
thisform.grdClient.Refresh()
thisform.grdClient.COLUMN1.SetFocus()

NB! This is only my personal opinion, but I find the -> construct "old" and difficult to read. Instead I prefer the newer point easier to read, like cusmas.cusno .

>Hi,
>
>I have a grid on a form and set the column header to BOLD, the caption is Customer Code, Customer Name.
>I have some code in click event on the column header, but after run the select statement, it reset all the setting of the grid,
>the header change to the cursor field name, not bold, the header click event reset to none.
>
>why ?
>
>the code as follow:-
>
>

>SELECT cusmas->cusno,cusmas->cusname FROM cusmas  INTO CURSOR cusmas_srh ORDER BY cusmas->cusno
>SELECT cusmas_srh
>GO top
>thisform.grdClient.RecordSource="cusmas_srh"
>thisform.grdClient.Refresh()
>thisform.grdClient.COLUMN1.SetFocus() 
>

>
>Please advise.
>Thank
>Derek