Sometimes you may run the Excel Extension and find it opens in two windows. One where you have the sheet and another where you have the edit options. This is caused by another application taking control of Excel windows before the Excel Extension can. To fix this follow the steps below:
Open Excel and go to FIle>Options>Trust Center>Trust Center Settings
Select 'Trusted Locations'
Browse to the locations suggested except for the entry for the Excel Extension
Delete the files mentioned.
This will ensure Excel Ext has priority in Excel and work correctly.