The "Undefined Error Hs Occurred" error means that there is a problem with the Site settings for connecting to the Testing server.
Double check the site settings and make sure that the settings for the connecting to the testing server are correct.
If you are using an FTP connection to use the remote server as the testing server, you may need to enter a root directory if the connection does not go directly to the site root.
and make sure that the WebURL is the correct Web Address to connect to the server.