I tried using backup and got the "move documents folder back to default location" message.

I have muddled through online support for 2 weeks to no avail... they sent an email saying to move dropbox back to C:\ and documents folder back to c:\users\dougt which should be  my default location . They then sent reset instructions :

Since the default location was the C drive, could you please move them back to the C drive? If you continue to receive the same error, please follow the next steps:
 

1. Click the Dropbox icon in your system tray. 
2. Click your profile picture or initials.
3. Click Preferences.
4. Click the Accounts tab.
5. Press the Alt+H keys and at the same time click the Reset OS folders locations button.
6. Click Continue.
7. In the pop-up window, click Continue to reset your OS folder to their default location and stop backup to Dropbox.

 I did this reset and then did a trial with just a few files in documents folder  and it worked . Then I moved all my documents folder (164 GB (176,322,775,578 bytes) from another internal drive and I got the error  "move documents folder back to default location" again. Funny that the screen shot attached to this shows folders in my documents folder but it omits some large folders. Is it because some are too big? And it is seeing the documents folder but returns the error? HELP PLEASE BEFORE I GIVE UP