I don't need to explain my issue its exactly like yours. EM started to give me this error out of the blue this past weekend. A second machine on my network for which I had not touched EM in over a month is also experiencing the same exact problem.

I am on Cox cable and they have said they are not blocking port 1433. One of my hosts says they they are able to get in on my account with EM. I can't access either of my SQL Server accounts with 2 different providers.

No new software, the only thing left is a router which has not been touched. Maybe if we compare notes we can find a common link that is the cause.