From here: https://forums.asp.net/t/1740537.aspx?Microsoft+Excel+cannot+access+the+file+is+solved+by+creating+a+folder

These are the steps for resolving the issue. If I ran Task Scheduler on demand it worked, but it would not interact with Excel of it was Triggered by the timer!

Run> dcomcnfg

This will open Component Services and navigate to Console Root
\Component Services\Computers\My Computer\DCOM Config\Microsoft Excel Application
Right click Microsoft Excel Application and select Properties

Click on Identity Tab and check selection.

It works for me when select option - The interactive user