I believe that you forgot to include the "Open Excel Worksheet" VI. I tried to open these to test them but that subVI was missing so I can't run it. One suggestion I have would be to purchase the Report Generation Toolset for Microsoft Office. This toolset includes Office specific VIs that perform all of the ActiveX calls for you. It makes life much easier when you are working with Office fairly often. Without being able to run your code, it's a little difficult to guess what might be happening. However,
here is an example VIs from NI's website which might help you out.
J.R. Allen