I have had the same problem. I also upgraded my computer from Windows 8.1 to Windows 10. After the upgrade I noticed that if I tried to transfer my files on Sansa Clip from the eaudiobooks folder to the audiobooks folder I got the message Sansa Clip is Busy.
I followed the advice and switched mode from the mode I was using Windows 8.1 to the other mode. This did not work.
Finally I got an idea. I took and Sansa Clip and attached it to a computer running Windows 7. I was able to transfer the files from EAaudiobooks to Audiobooks.
Please note that I did send an email to Sansa Support and as of a week ago, I received no reply.