Thanks a lot I could resolve this using:

//According to https://winscp.net/eng/docs/rawsettings this is how you set up the Preferred SSH protocol version under .net assembly
//...0-5 = SFTP version number
sessionOptions.AddRawSettings("SFTPMaxVersion", "3");

Thanks again,

Gabe.

Please read documentation:
https://winscp.net/eng/docs/rawsettings

Trying to access a host via SFTP I'm receiving the following error:

"Error: WinSCP.SessionRemoteException: No connection.\nError code: 6\nError message from server: [2015/12/15 17:40:55.977]
SSE2636 Command rejected due to sftp proxy policy settings: SSH_FXP_INIT ---> WinSCP.SessionRemoteException: Cannot initialize SFTP protocol. Is the host running a SFTP server?\r\n --- End of inner exception stack trace ---\r\n at WinSCP.SessionLogRe

Trying from the portable exe I was able to log to that host but after I change the setting of "Preferred SFTP Protocol Version" from 6 to 3.

Now the question is how can I set that setting from the c# call ?

Thanks in advance,

Gabe Gramajo.