>i am still with old vfp6. thanks all for you suggestions.

Good old VFP6 has GridHitTest(). In VFP5 it needs further math :

*VFP6 and later
*BRCC
Lparameters nColIndex
Store 0 to nWhere, nRelrow, nRelCol
* if would check mousedown outside grid (GridHitTest() returns .f.)
If mdown() ;
    and This.GridHittest(mcol(wontop(),3), mrow(wontop(),3), ;
        @nWhere, @nRelrow, @nRelCol) ;
    and nWhere = 3 ;
    and this.RelativeRow # nRelrow
  llLetItGo = ( nRelrow % 2 # 0 )

  Wait window 'Attempt to move from row '+;
    trans(This.relativerow)+;
    ' to '+;
    trans(nRelrow)+chr(13)+;
    'Will '+iif(llLetItGo,'','not ')+'let it go' timeout 2
  If !llLetItGo
    Nodefault
  Endif
Else
  If inlist(lastkey(),24,5,18,3,141,145,148) && 148 - Special case Ctrl+Tab
    Wait window 'Changing row with keys' timeout 1
  Endif
Endif

Cetin