Path Not Found Error

New user here just working through the tutorial  https://www.dropbox.com/developers/documentation/dotnet#tutorial  When I generate a token using an app for Full Dropbox, it works OK.  However, if I generate a token using an app for an App Folder only, I get an error that the path could not be found when calling download.

Here is my test code.  I've tried replacing "/HappyOtterInstaller" with "", but I get the same error.  Could you point me in the right direction.  Thanks.

wayne

using (var dbx = new DropboxClient("blahblah"))
            {
                var full = await dbx.Users.GetCurrentAccountAsync();                
                Console.WriteLine("{0} - {1}", full.Name.DisplayName, full.Email);
                Console.WriteLine("Press enter to close...");
                Console.ReadLine();
                await ListRootFolder(dbx);
                Console.WriteLine("Press enter to close...");
                Console.ReadLine();                
                await Download(dbx, "/HappyOtterInstaller", "currentBuild.txt");                
                Console.WriteLine("Download__Press enter to close...");
                Console.ReadLine();
                await Upload(dbx, "/HappyOtterInstaller", "currentBuild.txt", @"F:\ww.txt");
                Console.WriteLine("Press enter to close...");
                Console.ReadLine();
            }