I've seen other people in here get this bug, and now I have it too. It's where someone tries to summon you and it says "Summoning canceled. Unable to join multiplayer" and then you can't put your summon sign down again in that session. And then you reload the game and as you get summoned it says the same thing and you can't put your sign down again. Rinse and repeat. So co-op (and maybe invasions too?) is completely broken.
Feels bad man. Hope it's not permanent. Has anyone gotten this bug and had it go away? If so, how long did it take?
Now it says "Failed to create summon sign" when I try to put my sign down. Someone else is experiencing it here and it doesn't sound hopeful. If co-op/invasions for this character is broken, then fuck this game. I'm going to be too pissed to try a new character for a long time.