I recently installed a new FTP Server on one of my servers and could connect without issue and download files, but whenever I went to “PUT” a file, I’d get a 550 Access is Denied error.
After an hour or so of digging around (first wasting time on file system permissions and local computer firewall rules) I realized that the issue was my ISA 2006 server publishing rule. My rule was configured using the “FTP Server” Traffic rule:
What I had forgotten is that by default, when you publish an FTP site using this rule, it automatically sets another property (which is NOT visible on any of the properties tabs) to mark the FTP site as read only.
To get to the hidden property you have to finish the rule, then right-click it, and choose the “Configure FTP” Filter option:
You then have to clear the checkbox from the “Read Only” property:
As soon as that’s done, apply the rule and the file uploads will start working.
Darren Myher's Blog 