Can Not Edit Chart - Excel 2010

I have a workbook with one sheet of data and one sheet with a single chart. After creating the chart and modifying the format of the chart to the desired layout I saved and closed the workbook. Upon reopening it 15 minutes later i can now hover the mouse over the chart and I get a small black circle with a line through it indicating I can’t modify the chart. I can edit the data set in the data sheet and it gets plotted on the charts so the chart is active but I cannot edit the charts (axes, fonts, etc.). All of the edit buttons are greyed out when I look at the charts tab in the ribbon . The workbook and worksheets are not locked, protected, or read only.

Is the workbook 'shared'?

BSB