This will not help with problem, but may stop you chasing re herrings.
Quick google for FTP RFC SSL should find comment below.
Connect as usual to port 21 and use “AUTH SSL” or “AUTH TLS-P” to ask for SSL negotiation and implicitly protect further data connections. THIS IS BAD why ? (There is also a compatibility problem here, in that Tim Hudson’s original code gave a ‘334’ reply to AUTH SSL – this is now considered harmful and ‘234’ should be used. Clients are OK because they can accept both – but there still exist some broken servers which send ‘334’)
IBM are right, and wrong – Server should not be sending ‘334’, but their client should not throw a wobbly because it does. Believe only server spec was changed, so Client should still accept ‘334’. Unlikely you will convince IBM to change there Client, so best hope is to find updated server version, or go with different server software.