Two clients signed up for 2 different web hosts, and Dreamweaver had a problem with FTP for both. Many forums blame it on Dreamweaver, but for me the fix was to reset the FTP password.
Web host documentation says:
FTP Password: Your hosting account password.
It does not mention going into the FTP user and setting it. For NetworkSolutions, I simply re-entered the hosting account password. For GoDaddy I tried the same, but it claimed that it was not secure enough. Adding a punctuation character at the end solved the problem.
I searched for help from many forums and blogs but found no mention of this simple fix for getting Dreamweaver (CS4) FTP to work.