Can't add a specific friend

I used to have this person on my friends list for years then, one day it removes him off my friends list. I tried to add him again and it gives me the message off xbox can't do this at this time. When in a party I can't hear him and he can't here me, yet
everyone else can hear both of us. We tried several things and can figure out a way to add each other. We both Don't know what to do?

:)

 

Can't add a specific friend...

I'm trying to add Trepidwinter256 to my friends and I keep getting the same error message :

Sorry, we could only save some of your changes. try saving again.

I can add other people and remove them as well. It seems the problem is specific to that gamertag.

Thanks.

 

I can't add a specific friend!

Whenever I add a certain friend, it doesn't allow me to add him, and when I'm in a party with him, I can't hear him and he can't hear me, but someone else in the party can hear both of us. How do I make it to where I can hear him again and be able to add
him as a friend?