I am using following piece of code to update a chart,

ActiveChart.SeriesCollection(4).ChartType = xlLineMarkers
ActiveChart.SeriesCollection(4).AxisGroup = 2
ActiveChart.SeriesCollection(4).XValues = rng1
ActiveChart.SeriesCollection(4).Values = rng11

where rng1 & rng2 are calculated dynamically using the following piece of code:

Set rng1 = Sheets(inputSheet).Range(Sheets(inputSheet).Cells( iRow1, 1), Sheets(inputSheet).Cells(iRow2, 1))

Set rng11 = Sheets(inputSheet).Range(Sheets(inputSheet).Cells( iRow1, 158), Sheets(inputSheet).Cells(iRow2, 158))

The problem is sometimes this works, but sometimes it doesn't. It doesn't throw an error but I can't even see the plot though value is present. I am using XL 2003. Please help as this is too urgent!!!