The file or directory is corrupted and unreadable

When I open a folder in my computer, I saw the message

"C:UsersJohn SmithDropboxmyfolder1 is not accessible. The file or directory is corrupted and unreadable."

Fortunately, all files in this folder are on my Dropbox account. I copied this folder on Dropbox.com and made a duplicate folder names 'myfolder2.' Now this 'myfolder2' is accessible both online and on my local computer.

Then when should I do to 'myfolder1' folder?

(I'm using Windows 7 64-bit)