Comment 1 for bug 215522

This sounds like a response that we didn't expect.

Specifically, when auto-packing, we will clear out any packs that are in "obsolete_packs".

It sounds like your ftp server raises an error when you do "ls" in an empty directory. I would have expected it to just return an empty list.

Can you describe what FTP server you are using, etc?

450 seems to be "requested action not taken" which seems an odd error to return on an ls of an empty directory.
http://www.the-eggman.com/seminars/ftp_error_codes.html

Anyway, it would be easy enough to adjust the FTPTransport.list_dir() code to check for 450 and "No files found" and just return an empty list rather than an exception.