Never mind - I found the problem. Sorry for the post.

"Sam" wrote:

I have a simple stacked bar chart and wanted to remove one of the three
series. I did so using the Remove button on "Select Data Source", but after
I did this, I am now receiving the Invalid Reference error whenever I open
this chart. I have double checked the data behind the other 2 series and it
is all valid. How can I find the invalid reference?