Shivan, there are two social issues right now.
-
After a Maint cycle a couple months ago there have been issues with player detection as seasonal/non seasonal, and other grouping issues. Players CAN make a solo game though. That is being tracked by Blizz on the General forums. Last blue post this week S-19 Group Join Bug - #84 by Matthew_Cederquist
-
Starting in Oct players who were Muted in Blizzard games can’t make a game at all. The button says only party leader can make one, but that is not actually true. At first they thought it was connection related, but realized later it was indeed Silenced players. This is being tracked in a thread on the TS forum. The last Blue reply to that was this week Start Game Greyed Out - Unable to join game, only available to party leader - #295 by Drakuloth
Are you silenced in any Blizzard games? If so that is what is going on.
We had a brief issue yesterday with similar symptoms that was unrelated to either bug, but that cleared up in about 45 mins.