I had same problem after fresh install. Went to system video add ons, Xuninty maintenance fixes 1channel proxy fix or domain proxy fix or both can't quite remember.
Restarted xbmc went to video add ons and waited couple of minutes for add ons to update then M box worked for me then.
If anyone else can advise first be a great help as this is new to me and I'm not sure if that's the reason it worked for me or if m box just wasn't working for a short while ?
I wouldn't want you to cause yourself anymore trouble ;-)
Sorry I can't help much more than that I'm afraid if helping at all ?
Regards Justin.