After a slug of bourbon and some more digging I think I found the problem. Hot NAT on NAT action, which PHP ftp doesn't necessarily play well with UNLESS you set this flag - FTP_USEPASVADDRESS - to false immediately before making the connection pasv. I tested it ONCE and my test script worked on the...
Just swinging back to this now. Dedicated, unmanged are fine, as stated before, as are other non-NFO servers I've tested. But - these Managed VDS's... appears you are running vsftpd right? When I throw an ftp_systype() at this I get: 500 OOPS: vsf_sysutil_bind - all other servers tested everywhere r...
I can't see any reason for this to fail other than some firewall or other hitch on the NFO side. Using basic PHP FTP calls: ftp_connect, ftp_login, ftp_pwd, ftp_pasv, and so on. Code works fine on publically available FTP test servers. Works perfectly fine on our Unmanged VDS with PureFTP installed....