Try changing it as follows :

LOCAL lnOldSelect, lnKounter, lcControlSource
lnOldSelect = SELECT()
lnKounter = 0
SELECT GridColumns
WITH MyGrid
.ColumnCount = RecCount() && THIS IS THE BIG CHANGE
.RecordSource = pcTableName
SCAN
lnKounter = lnKounter + 1
.COLUMNS(lnKounter).Header1.CAPTION = GridColumns.ColumnName
.COLUMNS(lnKounter).READONLY = .T.
lcControlSource = pcTableName + [.] + ALLT(GridColumns.GridColumn)
.COLUMNS(lnKounter).CONTROLSOURCE = (lcControlSource) ENDSCAN
ENDWITH
SELECT (lnOldSelect)