Hopefully my reply posts, quickbooks forums dont seem to allow any correct answers to be posted.  Excel has very minor bug where you cant open another excel file unles you clock on a cell in an excel file you already have open.  You can sit thre for 5min and nothing will open, but when you click in a cell of an open worksheet, the one you want to open will open up like clockwork.

I had your same issue, even a report I just pulled, it wouldnt let me open again.  I clicked on a cell in the report I had open, went back to QB to pull the failed reports, and finally I could pull a report with no errors.