I had same issue but with Win 7. I got mine to work by searching for the FTP site in the registry and deleted it.
Searched using EDIT , FIND , ftp.whatever.com , clicked FIND NEXT
(Found in HKEY_CURRENT_USER, Software, Microsoft, FTP, Accounts )
Right-clicked the FTP site giving me problems (ftp.whatever.com) and deleted it.
Fired up Windows explorer: prob solved.
You might wanna give that a try.