From time to time opening FTP connections in Finder results in error messages that don’t reveil much about the cause of the error. What I see most often is “The Finder cannot complete the operation because some data in (address) could not be read or written. (Error code -36).” What is Finder trying to tell me? I found a hint that including the user name in the FTP URL usually fixes this problem. So, instead of ftp://myurl.ch, you would connect to ftp://myuser@myurl.ch. It’s a valuable hint, indeed. It fixed all my connections problems at least.
Btw, don’t worry about including a “secret” user name in the URL. It’s not less (in)secure than without. Standard FTP sends user name and password in clear text across the wire anyway. If this bothers you, don’t use standard FTP.

By coincidence the very same URL that caused problems in Finder (see above) gave me a headache when I set it up in Adobe/Macromedia Dreamweaver. I can’t remember the exact error message, but whatever I tried the connection couldn’t be established. Dreamweaver only reported that I might try to switch on “passive FTP”. However, when I checked my System Preferences (Network -> choose your connection -> Proxies) I found that PASV was already activated. What the Dreamweaver team failed to mention in the error message is that the Dreamweaver specific “passive FTP” switch is only available in the advanced configuration dialog for your sites. At least in the OS X version of Dreamweaver that small Basic/Advanced button at the top of the dialog is so small that it can easily be missed.