I am totally alien to 2013, but I seem to remember that if , in 2010, one wants to open sheets in different Excel sessions,under Excel Options - Advanced - General, one should check " Ignore other applications....(DDE)".
Maybe unchecking this in 2013 might help?

( I also may be totally beside the point...)

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I just twigged. I apologize, jread47; I read your posts, I promise I did, and you wrote "2013" at least twice...many times, I see now that I look more closely...but until Peco's post, all your "2013" repetitions went right over my head. Please forgive my carelessness. I have nothing useful to say about 2013.