Unfortunately the unidentified error is a problem that occurs from time to time when creating a connection inside of DW. To try and resolve the issue you should make sure to delete your connection from within DW. Next you should clear the cache file for DW with these instructions:
It would also be worth deleting your _mmServerScripts folder from your site root in case there is any bad connection info in there. Once you have done these things try creating the connection again and testing it. When it comes to the db name try entering one in rather than using the select button.
Also, you should confirm with your host that remote access is allowed for connecting with the MySQL db. It is very common to disable remote access and force only local access to the MySQL server. It seems like you host may have it setup for you to access based on what you posted here but it is something else to check.