Maybe...

http://contextures.com/xlfaqApp.html#AlreadyOpen
From Debra Dalgleish's site.

Jocco wrote:

I am using Excel 97. I had to re-install the program. Now when I double click
on an Excel file in Explorer to open it (without Excel being open), I get a
message that the file is already open. If I click OK, it opens without any
problem. Is there a way to eliminate this nuisance message?

--

Dave Peterson