If you're getting the "Unable to resolve remote host name" error, it means the host name entered in the connection profile dialog is incorrect, or there is some problem with your ISP's DNS servers, or your computer. One way to verify this is as follows:

Select the hostname in the connection profile dialog, right-click it and select "Copy".
Open a Command Prompt window.
Type "ping " (without the quotes), then right-click on the command prompt window title bar, and select "Edit -> Paste". You should end up with something like this: ping mywebsite.com
Press ENTER. If it says "Unknown host", this shows the host name is incorrect, or there is some other problem. If it says "Pinging mywebsite.com", then gives a few lines of statistics, the host name is correct and the problem is elsewhere.
If the host name was pingable but still fails to connect, see below
Try checking the "Passive Transfer" box on the Firewall page of the connection profile screen if you have not already done so.

If this does not help, try checking your internet connection settings for a default connection. If you have recently switched to a DSL or Cable connection your old dial-up connection may be referred to as the default. In that case, open Internet Explorer > Tools > Internet Options > Connections > and select Never dial a connection > select Apply > then select OK to close this dialog.