When you change the RecordSource of the Grid, You need to redefine the controlsource of every column. Try something like

SELECT NewTable
WITH THISFORM.Grid1
.RecordSource = "NewTable"
.ColumnCount = FCount()
FOR n = 1 to .ColumnCount
.Columns(n).ControlSource = "NewTable." + FIELD(n)
NEXT
.REFRESH
ENDWITH