The survey may contain invalid data that is causing this error. Try reviewing the survey, especially in External CSS and Javascripts, and making sure all questions and responses are properly formatted and do not contain any errors. Please clear cookies and try to copy it again

Hi Vinoth_Mathaiyan , thank you for your very speedy reply!
I tried clearing my cookies, but nothing changed. I checked the question & response formatting, but didn't find anything obvious. As for Javascript and External CSS, I haven't done any editing with either of those, and I'm not sure how to even look for errors in that area. I did go into the Javascript editor for a random selection of survey questions, but there didn't seem to be anything there.
Fortunately, I had a draft copy of the survey in another project folder, and was able to copy that version successfully. So my original problem remains unsolved, but my work flow has been fixed!

I am also having this same problem and cannot seem to resolve it either.  

Mary