I have been able to connect on xbox live before to this person but now i cant?

i have been able to connect to my friend on xbox live sense i got my xbox a month ago i don't know what happened but the other day we were in a party and it said cant connect to xbox live party he claims there is nothing wrong with his network connection and same with me it says im connected to everything but still i tried un plugging my xbox i tried doing xbox live tests i tried clearing the system cache but nothings working does anyone have any suggestions to help me please help if you may know what the problem is!!!