You'd have to edit the source code if you want to "supress" the error. However, you're just hiding the problem. The password will still be available to be read by anyone. My advice is to either use an "anonymous" ftp account (i.e. no password) or use an HTTP server to host your updates. HTTP is faster and you have much more flexibility.
If you need to limit who gets what updates then this is a good place to start: How to prevent or limit updates.