I've seen this before when all the references to Excel have not been closed properly from the last time it was run.
The ActiveX examples that ship with LabVIEW and on our website are very good starting points, but if you are going to use LabVIEW to manipulate Microsoft Word and Excel, I really suggest getting our Report Generation Toolkit for Microsoft Office. The RGT (Report Generation Toolkit) contains a complete set of easy to use VIs to programmatically create and edit Word and Excel documents. The Microsoft Office ActiveX interface is huge, and it is often times hard to find good complete documentation on how to perform certain tasks. The RGT VIs hide all of the ActiveX complexity and really simplify the tasks, but as a developer I really appreciate t
he fact that the VIs contain all of the ActiveX code on the block diagram so that I can look at them as examples and modify them to my desire. You can find out more about the RGT from ni.com, click on Products, LabVIEW, LabVIEW Addons, LabVIEW Toolsets, LabVIEW Report Generation Toolkit.