If the workbook is password-protected, then that would cause Excel to
pop up an input box for the password. (Even though you have
DisplayAlerts set to False). There are probably other obscure reasons
why this could happen.

You can get around the password problem by supplying a (wrong) password
in the Open call - in which case an Exception will be raised if the
workbook is password protected, otherwise the password will be ignored.


Why not try making the Excel app visible, so that you can see exactly
what Excel is doing?