Check under File, View All Users to see who is using the file.  If you only see one user then try the following.

First open Sage 50 and then open the Sample file.  Allow it to convert to the current version if it requests it.

Then close Sage 50 completely.

Then try restoring your file again.

Thank you.  Tried both to no avail.  However I did have success by doing both of the following: 1) run as Administrator and also this  2)  the file that I was trying to update would not open when I attempted the Restore on the entry screen.  However, I could simply open the company file, THEN do RESTORE with the file already open.  No idea why.. but the update of data did work!

This is one area where the "Fast-Open Technology" built into Sage 50 fails.  Sage really needs to fix this.  I guess opening of the sample file does not reset the Fast-Open Technology so it didn't work for you.  I guess that makes sense now that I think about it more.  Glad you figured it out.