I've used BrowserLab in the past without a hitch. I have been trying to use it for the past couple of days as follows:
I choose File > Preview in Browser > Adobe Browser Lab from the DW menu. I checked the Browser Lab panel and I am trying to view my offline files via Local/Network. BrowserLab does open in the browser (I've tried Chrome, Firefox and Safari, obviously I am working on a Mac). I can log in with my Adobe ID. So far everything seems fine. But then I get there and all I see is a grey page. There are menu items at the top of the page for choosing a language, establishing browser sets and reloading, but that's it. The main area of the page is nothing but gray. I tried to refresh and received an error message that no browser sets were selected. I tried to create a new browser set (I chose a few browsers and pressed the Add Browser Set button) but nothing seems to happen. I don't see any indication of a new set being created and when I try to refresh again I get the same error message about not establishing a browser set.
I tried going through the BrowserLab panel in DW but the same thing happened. In DW the panel displays an error message: Timed Out, failed to connect to BrowserLab (even though it seemed like I was basically seeing BrowserLab, just not able to use it).
The other thing that is weird--it almost seems as if for just a quick moment I can see that BrowserLab tries to display my page before it goes gray.
The offline file has been validated (HTML5 and CSS) and I can see in File > Check Page > Compatibility that there are no issues detected. So I'm fairly certain that I'm dealing with pretty clean code.
Finally, I did check for new updates and updated Dreamweaver to CS5.5 yesterday. But, I'm still having the same issues.
Have you tried deleting your browser cache/cookie to see if that helps. please try that and please let us know if that fixes the issue or helps you move forward.
one other thing to try these steps in the following sequence
please let us know if this works for you.