An error occurred opening that folder on the FTP Server, Make sure you have permission to access that folder

The error is 'An error occurred opening that folder on the FTP Server, Make sure you have permission to access that folder. Details: The connection with the server was reset'. Here's a few behaviours we've seen so far:

Case 1: Going to ftp.nospy.com gave the error but going to ftp.nospy.com/nospy was fine. Then going back to ftp.nospy.com was fine too.

Case 2: Opening ftp.nospy.com in IE was fine, but then opening it in Windows explorer gave the error.

Case 3: Browsing ftp.nospy.com/nospy was working fine, but then browsing into the /content sub-folder or /shareware sub-folders gave the error. Browsing into the /builds folder worked fine, and then browsing back into the /content or /shareware subfolders were fine too.

Solution:

Update the proftp packages by hitting the commands apt-get dist-upgrade then it will prompt for a step by step instruction (default setting is still the best for it)