Login issue

I have used several different ftp clients without any issues until now. I tried smartftp and any time I try to log into one of my sites I get the following:

[22:29:10] SmartFTP v2.0.997.4
[22:29:10] Resolving host name ""
[22:29:10] Connecting to Port: 21
[22:29:10] An invalid argument was supplied.
[22:29:10] Cannot login waiting to retry (30s)..

What is the issue?