In a lot of cases you will get this error if you don't have your Site Definition set up correctly and specifically it you don't have your Testing Server Set up to point to the correct folder on your testing Server.
also, it seems that deleting the DW cache file or recreating the Site help to fix the issue.
If you are still getting the error, you can download the attachment in the following thread which will allow the Wizard to continue after you click OK to generate the required pages:
showthread.php?t=23795