The FTP protocol predates UTF encoding. Switch to ANSI/ASCII for better results. If you do opt for writeMultiByte instead of writeUTFBytes, be aware that it is buggy in linux. Here's one way around it.
There's another question here where the line ending turns out to be the culprit, so make sure that you get it right (as suggested above).
As said before, if this is running from the web, all socket connections will require a crossdomain policy, but this is NOT file based over HTTP. Recent changes to the security rules mean that any socket based connection must first get a crossdomain from a policy server hosted on port 843 of the target host.
Quoting from Adobe:
A SWF file may no longer make a socket connection to its own domain without a socket policy file. Prior to version 9,0,115,0, a SWF file was permitted to make socket connections to ports 1024 or greater in its own domain without a policy file.
HTTP policy files may no longer be used to authorize socket connections. Prior to version 9,0,115,0, an HTTP policy file, served from the master location of /crossdomain.xml on port 80, could be used to authorize a socket connection to any port 1024 or greater on the same host.
Essentially, what this means is that you must be in control of the target FTP host, and install supplementary software on it to get this working.
