the unidentified error means that either there is a problem with the Dreamweaver Site definition, specifically in the settings for connecting to the testing server.
Go to Sites -> Manage Site
select your site and click edit.
if you are using DW CS5.x Go to Servers, and edit the one that has the testing check box selected.
in DW CS 4 or lower, make sure you are using advanced view, and select the Testing Server category.
What are the settings you have entered for connecting to the testing server?
Are you connecting to a local testing server or a remote testing server?
do you have the correct address entered for the URL Prefix (Web URL in DW CS5.x)?
If you are using the remote server as your testing server, is the host directory set correctly? this should be set so it maps to the same location as the Web URL.
for example, if you connecting to the server through FTP, you may be connecting to the server in a folder below the webspace, you may have a folder named htpdocs which is the folder that your webpages are served from, if this is the case, make sure that you enter that folder in the host directory setting so that the connection made by dreamweaver is to the same location as the web url,
