Connection from mainframe ended by Core FTP server: Reason 2: connection type not allowed

[dennisjm]

I have a client running on an IBM mainframe that is trying to connect to a Core FTP server for the first time.
Debug output on the mainframe shows this version information for the Core FTP server: SSH-2.0-CoreFTP-0.3.3.
Debugging shows authentication was successful, a session channel was open, then the client sent a sftp subsystem request.
The Core FTP server disconnected with the client logging this message:
Reason 2: connection type not allowed

Does that reason indicate the Core FTP server is not configured to handle sftp connections from that client?
Which areas on the Core FTP server should I check? Site Manager? Connect Manager?

Are there any diagnostics on the Core FTP server which can provide more information on why the server disconnected?

[ForumAdmin]

the only subsystem type allowed is 'sftp'. All other connection types will be rejected. Good chance the client is requesting a shell session.