Me NA and my friend EU can’t play in nightmare mode together however we can play just fine in normal mode.
we level up a warlock together in normal then we tried nm but got the error above when me or him tried to join the other person.
I then tried to rush his wizard that was lvl 20 but that did not work same error afterwards.
please advise
had this same issue the other day rushing a buddy
And additional information is that when he looked at the list of available games in nm he saw about 10 while I was seeing 40+
Make sure you two are in the same server region. That’s fixed my issue. My mate was in the asia region, I was in the Americas. When I set my one to her region, it worked.
Thats not an option on console, region is locked to account region but crossplay has never been an issue
same issue here, but it’s weird because I was able to play with this same friend in level 1 while creating a new char. We just can’t join each other in hell difficulty with hold char before Warlock came out 
I’m in NA and my brother is in EU and we get the same message. “Unable to enter game. Your character mist kill Ball in a nightmare game.”
Bro, this IS nightmare. Even after killing Baal in a nightmare game (we both did), we still get this damn message.
I swear, blizzard is making it harder for us to play by the day, before it was the bullcrap of not being on the same level, we finally got around that just to get stuck with this stupid crap.
Blizzard, any word? This is on console, so please don’t give me the pc treatment here.
Same let me know if you find a fix
Im having the same bug. What could be the issue? dont understand how they cant keep a game running
same here, my friend in Japan, and I’m in NA, we can’t join the hell game. Said must kill nm Baal. Blizzard, plz fix this.
Same issue. The error message is misleading. My buddy and I were on difference servers.