Windows 7: You Need Permission to Perform This Action

I was trying to move a file from one folder to another.  This was a frequently used folder.  I had done this operation a thousand times before.  Suddenly I got this error message:

Destination Folder Access Denied
You need permission to perform this action

A search led to the suggestion that, in Windows Explorer, I should right-click on the folder and go to Properties > Security tab > Advanced > Owner tab > Edit > select Administrator (since that was who I wanted to own the folder, though that was *already* who owned it) > Apply > OK.  That didn't work.  Some remarks indicated that this could be a digital rights management issue, in the case of a music file, but this was just a PDF.  It was, however, a PDF created by Sumatra PDF, in an attempt to remove security from the PDF so that I could run OCR on it.  It seemed I should have used Foxit instead.  Anyway, I went back into Properties > Security tab > Advanced > Everyone > Change Permissions > Everyone (check both boxes) > Apply > OK.  That didn't do it either.  I moved everything out of the folder, deleted it, put its former contents into a new folder, and was able to work normally.  No explanation.