It's not really a problem with SME, as one machine connects, so you shouldn't be asking in this forum.
With that out of the way, try disabling the McAfee (right clicking on the task tray icon is a start) to see if you can disable it, then see if things work. Sorry, don't know the product well enough for a step by step, go to their website. That will determine if it's that that is causing the problem. Otherwise it may be something else, web browser settings perhaps.