Diagnose Connection Problems??

I have been getting this error for the past few months. I thought it was because of AT&T, but I have switched to Clear and still get the message periodically,though not as much. When I click the button on IE8, a window will pop up to “diagnose” the problem, and in the background the page I was trying to open will appear then. And the diagnose connection problem window will say that it didn’t find any problems after I push the button. What’s really going on? Is this a networking issue or a MS issue. P.S. I put a new ethernet card in a couple of weeks ago, so I don’t think that’s the problem.