Maybe the answer is at Debra Dalgleish's site:
http://www.contextures.com/xlfaqApp.html#AlreadyOpen

p16ande wrote:

Every time I open an Excel document I get a message that states "The document
with the name '@#$%' is already open. You cannot open two documents with the
same name even if the documents are in different folders. ...." Since I do
not have any documents open, what do I do to get rid of this message?

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Dave Peterson