If you are getting the unknown error occurred error message you should try creating a new DW site and setting up a new connection. Do you know if your db can be connected to remotely? If your host has disabled remote access, which is very common, you will not be able to access the db from within Dreamweaver.
It might be a good idea to setup a local testing server if this is the case, here are some links on this topic:
Setting up a testing server on Mac:
Setting up a testing server on PC: