There are about 3.5 million hits for [ftp message 550]. Looking at just a couple (e.g., from WS_FTP, or from a FileZilla forum) makes fairly clear that message 550 comes back from the FTP server that you connect to and it indicates that the server isn’t going to do what you asked it to do. The text (in your case “mysavefile: Access is denied.”) should help explain why.
You need to logon to your Win2000 Server to determine why it refuses to let you put the file. Maybe you don’t have proper permissions set on the file. Maybe you aren’t authorized to put stuff into the directory. Maybe you aren’t authorized to put anything to the server from FTP.
The FTP RFC-959 makes a definite statement that the issue is on the server.