put this code in BeforeRowColChange Event

lparameters nColIndex
Local llChangingRow,lnTop,lnBottom,lnMouseRowPos,lnMouseColPos
llChangingRow = .f.
With this
If mdown()
lnBottom = .top+.headerheight+.relativerow * .rowheight
lnTop = lnBottom - this.rowheight
lnMouseRowPos = mrow(wontop(),3)
lnMouseColPos = mcol(wontop(),3)
llChangingRow = !(between(lnMouseRowPos,lnTop, lnBottom) ;
and between(lnMouseColPos,.left,.left+.width))
Else
llChangingRow = inlist(lastkey(),24,5,18,3,145,148)
Endif
If llChangingRow
nodefault


*..

Only make nodefault if llChangingRow = .T.