Cannot Easily "Edit Data" in PowerPoint/Excel Graph - Please Help!

I am updating charts from an old 2003 version to the 2007 version. Here is what I have done:

1. Clicked "convert" graph (to 2007 version)
2. Clicked "Select Data" and I selected the data in my excel sheet that I want the graph linked to.

Now whenever I click "Select Data" the correct Excel Sheet, call it Book1.xls, comes up, but if I edit it the graph does not change, I have to reselect the changed data.

Whenever I click "Edit Data", a new excel sheet "Chart in Microsoft Office PowerPoint" comes up, but nothing I do to this sheet does anything to the graph, in fact - I deleted all data from this chart, and now when I click on "Edit Data", this blank sheet always pops up.

My goal is to have the correct data, which currently shows up when I click "Select Data", to come up when I click "Edit Data", so that when I edit this sheet, the graph will update with it. I do not want to have to deal with this extra excel sheet "Chart in Microsoft Office PowerPoint", I want the graph linked to the data in Book1.xls.

Thank you, in advance, for your help. It is greatly appreciated!