Maybe like this :

ActiveCell.FormulaR1C1 = _
"=UPPER(TEXT(INDEX(Sheets(" & myValue & ")!C[-2],COUNTA(Sheets(" & myValue & ")!C[-2]),1),""mmmm d, yyyy""))"
and

ActiveChart.SeriesCollection(1).XValues = "=Sheets(" & myValue & ")!B2:B500"