My extra window turned out to be a problem with add-ins. In Excel 2010, here’s how to fix that:
- Open Excel.
- Go to
File > Options. - Click on
Add-ins. - Look at the Active Application Add-ins
- At the bottom of the dialog, in
Manage, set the dropdown to COM Add-ins and click Go… - Uncheck the things you don’t need.
In my case, there were three COM add-ins active:
- MySQL For Excel
- DriveForOffice [Google Drive add-in]
- Microsoft Excel Code Compatibility Inspector
MySQL for Excel was the culprit.