AppCmd 80070057 errors when configuring site-level settings

I had an interesting question from a coworker who was trying to use AppCmd to set the site-level SSL options for an FTP site. This should have been straightforward, and the syntax that he gave me looked correct:

appcmd.exe set config -section:system.applicationHost/sites -[name='Default FTP Site'].ftpServer.security.ssl.controlChannelPolicy:SslAllow /commit:apphost

That being said, whenever he or I ran the command we received the following cryptic error from AppCmd:

Failed to process input: The parameter 'Site'].ftpServer.security.ssl.controlChannelPolicy='SslAllow'' must begin with a / or - (HRESULT=80070057).

The HRESULT=80070057 code can mean either "One or more arguments are invalid" or "The parameter is incorrect", which seemed wrong to me because the arguments looked correct. Based on the error message referring to the word 'Site', I retried the command using the site ID instead of the site name:

appcmd.exe set config -section:system.applicationHost/sites -[id='4'].ftpServer.security.ssl.controlChannelPolicy:SslAllow /commit:apphost

This worked as expected, so I knew that somehow the problem was with the site name.

I searched around and I found a forum post on IIS.NET where Anil Ruia had stated that when the site name has a space in it you should enclose the entire parameter statement in quotes. Armed with that knowledge, I tried the following command:

appcmd.exe set config -section:system.applicationHost/sites "-[name='Default FTP Site'].ftpServer.security.ssl.controlChannelPolicy:SslAllow" /commit:apphost

This fixed the problem and the command worked as I would have originally expected.

By the way, in general you should be able use the following command to get the FTP syntax listing for an area:

appcmd.exe set config -section:system.applicationHost/sites -? | find /i "ftp"

This wouldn't have helped my coworker identify the problem with the "name" parameter, but it would have helped by giving him the syntax for using the "id" parameter.