"Error: Could not establish a web session. Please try again."

I was having a problem as well. My launcher wouldn’t update. I uninstalled it and reinstalled it and nothing worked. I couldn’t open anything up in the marketplace. So I just downloaded the new version from the site. After it installed I ran the launcher and it said there was a shortcut that was out of date and gave me the option to fix it. I did and now my launcher works like it should.