Inbound SFTP connection is failing for customer

Customer has a connection set up to connect to an ISC sftp server but it keeps failing the connection with:

ERROR <Ens>ErrOutConnectFailed: SFTP Connect failed for sftp.il.intersystems.com:22/NPPES/SSL='!SFTP'/PubKey=''/PrivKey=''
with error ERROR #7500: SSH Connect Error '-2146430933': SSH Error [8010102B]: Failed getting banner [FFFFFFFF8010102B] at Session.cpp:238,0

A manual connection can be made successfully and I have verified that the credentials are correct. The Connection Settings are:

SSL Configuration - !SFTP

UsePASV - checked

I'm not sure how to interpret the error.

Thanks,

Steve Diquattro