Message: Ref not Valid. Must be to Open Worksheet
 

Hello,

I've copied a chart into a new worksheet and then attempted to modify the
series data to point it to new data. When I try to make the change, I get
the message:
Reference not valid. Reference must be to an open worksheet.
I've looked at the worksheet and it is not protected. Can someone help me
understand how to make modifcations to this copied chart data?

Thank you